I don’t have Alexa integration for Sonos being in India, and someone will come around here with all the steps necessary for you to set up this for your Alexa. Essentially, there is a one time set up to be done within the Sonos control app as well as enabling the Sonos skill in Alexa which you seem to have done, but there must be some little detail left.

But, even so, you will not be able to “amplify” what you are playing and seeing on the Show. Sonos will only take a voice command from the Echo Show and play what is commanded, but what is playing will not be seen on the Show.

Unfortunately, you need Sonos kit with line in jacks to do what you want - via wires running from the Show to the Sonos line in jacks. Sonos then will play what Show is showing.

There are 3 options when it comes to syncing  Echos with Sonos.

1 - Setup the Sonos  skill on alexa and do the integration as you mentioned.  You can then setup an Alexa group where your sonos speaker(s) are the prefered speaker for your echo show.  So whenever you request to play a music streaming service, the music will play on the Sonos speakers instead of your Echo show.  It will not play on both the echo show and Sonos.

2  - Pretty much the same as the above, but you can setup a default speaker for a particular echo device.  This means that whenever the echo hears a voice command, it will respond on the default speaker.  The catch is that the default speaker has to be an alexa enabled device, like a Sonos One, Beam, Move, or Arc, and it is not available on Echo Shows.  The reason is that the Show can’t show images on it’s screen and sync audio playing on another device. It does not matter if the default speaker you specific is Sonos, an Echo, or any other speaker, it’s not supportted for the Echo Show.

3 - The third option is what @Kumar suggested in his last paragraph, using a line in connection.  Besides having to physically connect Sonos and your Echo Show, this has a few other issues.  One is that your Echo Show won’t play audio as all the audio is sent to Sonos. Second is that Sonos is going to add a little delay for processing the audio, which means Sonos speakers will be out of sync with the video on the Show.  Last, you’re pretty much disabling any other ability of your Sonos speakers, since you would need them to be set to play line-in audio all the time.

To clarify some of the above, since I use this extensively and love the feature of seeing album art for all music that I play, something that Sonos simply cannot do on its own:

1. The video delay is too small to be intrusive is my experience. And for album art, this is not a relevant issue anyway.
2. Setting the Sonos speakers to auto play line in does not disable any other ability of that Sonos unit - except perhaps those related to independent voice control via Sonos of which I have zero experience. I still use my Sonos speakers with Echo Show wired to their line in jacks independently of Echo Show, with/without other Sonos speakers in a group, as I did before I wired in the Show unit. Although this kind of use is rare these days, since I much prefer the Echo Show as source route for most of my listening now, including for music from my ripped CDs.

The real issue here is that Line In jack equipped Sonos kit is needed for this to work. 

What I mean by this is that whatever Sonos speaker is connected to a Show via line-in (Amp, Port, Five and their predessors) will need to be set to line in all the time.  If you’re using a Five for example, and decide you want to play Sonos radio, or some other streaming service Amazon doesn’t support, or just group the audio from another Sonos speaker. then your Five won’t be set to line in.  If you speak to your Show while not in line in, you won’t hear it on your Five.  You could set it to autoplay, and it will switch to line in after a slight delay, but then you have disconnected from whatever you were listening to before. While perhaps not a problem if you intended to switch the audio currently playing, it would be rather annoying if all you wanted to do was turn on a light switch or hear about the weather and continue on with the music playing on your Five.

I’m not trying to downplay the value of album art or song lyrics. I just think that the cost of using a an aux line in between echo and Sonos has too many issues to be worth it.  The times I do want to see album art/lyrics, I’ll usually just use the Amazon (or other service) on the TV and stream to Sonos via that connection.

To each his own. I prefer the wired in Echo Show to anything that I have seen Sonos do via the Alexa integration that also misses out on album art. I also suspect that Alexa features implemented on Echo devices are always some steps ahead of those in the Sonos Alexa integration and the only way to get these as soon as they become available from Amazon is via line in.

I therefore see absolutely no issues in the line in route except the need for line in jacks - after having used that for a year now. Via these is also the only way that the OP stated need of not having Echo Show and Sonos as two separate systems are to be met.

And there is no cost to these except the few bucks needed for a simple cable, if one has the necessary Sonos units that will take a wired connection.

The Sonos One misses out by not having such a feature.

If you’re using an echo device, you’re getting the new features implemented, regardless of whether you’re connecting to Sonos via the skill or line in. I don’t get why you think you wouldn’t get those features, unless you were thinking of something specific to music streaming.

Well, if you ignore the fact that OP wanted her Echo Show and Sonos to play audio at the same time.

I think that Alexa skills on the Sonos Alexa integration lag behind those implemented by Amazon on Echo devices. Unless Sonos has become more agile in recent times.

My understanding of the OP need is for Echo Show and Sonos to play the same audio at the same time, all the time. Something that is only possible via Line In. I may have misunderstood the requirement, but I think that only the OP is entitled to say that I have ignored it.

With my Echo Show able to be the voice and cast commanded source for Amazon Music, Apple Music, Spotify and local NAS - and all with artwork - I see no need now to not use it as a source and go back to playing Sonos directly so the concerns then about the use of Echo show via auto play line in causing issues to such direct Sonos music play are not relevant in my case.

I see no point in continuing this conversation unless the OP has any questions that are posed that I can answer.