Issues with my setup and connecting a record player

No, there is no easy way to overcome the Line-In being deactivated on surrounds.  The alternative is to purchase an Era 100 and a Line-In adapter and use that for the Line-In (Note: Any Sonos Line-IN equipped unit will do the job, the least expensive is the Era 100 + adapter).

You could also purchase a turntable that streams wirelessly to Sonos, either via Bluetooth, the Victrola Stream models, or the new Pro-Ject W that was made for streaming.

I’ve maxed out the amount of components allowed in my current speaker system group.

You have hit the 32 device limit? 

If so then you are limited to using an existing non-surround Sonos with a line-in or removing one of your Sonos to open a slot for a new device.

​@Stanley_4, good point.  To the OP, by “maxed out the amount of components allowed in my current speaker system group”, do you mean you have the maximum number (32) of Sonos units, or that you’ve maxed out your “arc, two subwoofers, and the amp” room?

If the latter, it really doesn’t matter.  Any LIne-In source can be played in any and all rooms on your system.  Example: You could get a new Era 100 and a Line-In adapter.  You would connect your turntable to that Era 100.  You could then play the Line-In source on that Era 100 to any and all rooms on your system.  You could even set up the Line-In so that when you lower the needle on the turntable, it will automatically play to your arc, two subwoofers, and amp room by default, and the Era 100 with the LIne-In won’t be playing anything at all.

You could even name the Connect or Era Sonos Room "Turntable" no matter which room of your house it is in. 

I meant this:

A single Sonos "room" configuration typically supports a maximum of 

5.1 channels for home theater (soundbar, sub, and two surrounds). For music, a room can be a single mono speaker or a stereo pair. You can group multiple rooms together to play the same audio, but they operate as separate, synchronized units

that’s kind of why I was hesitant of getting an additional speaker just to get my original components to play from a record player.  It kind of just seems like a redundant thing that shouldn’t really have to be done especially when the amp already has a line in function.

It’s helpful to know what is at work when we say the Line-In function for the Amp is disabled when used as surrounds.  This isn’t some arbitrary decision by Sonos engineers. In a surround/sub configuration, to accommodate lip-syncing with the video, the Sonos radios are reconfigured to a one-way dedicated 5 GHz connection from the soundbar to the surrounds.  This one way connection allows for lower latency, but because it is only one way, the Line-In and Bluetooth connection on the surrounds is no longer active.

I suppose my ideal setup would be if it was easy to switch between surround sound/tv watching mode, and when I want to listen to a record and just have the music play from the speakers.  But it seems like I need to modify the speaker groups in the Sonos app each time to create that experience.

Again, because of the special connection between a soundbar and subs/surrounds, “easy to switch” is not really possible.  The switch reconfigures the radios and handshakes between the units to fine tune the connection, which is why adding/removing surrounds takes the time it does.  I suppose they could automate the process to one button press, but that won’t make it significantly faster. 

If they automated the process they would have to choose between swapping to a default configuration of all components in the set at the switch as is done now or dedicating a significant amount of internal nonvolitile memory to saving the configuration information to allow it to be restored. Possibly for multiple configurations?

The “auto” feature has often been requested on the forums, and has been noted as a feature request by Sonos staff. Don’t hold your breath waiting for it to be implemented though.