By ‘home theatre experience’ I assume you mean dolby digital 5.1.  The first part is connecting to your TV, and that can be done by HDMI-ARC or optical (via Sonos optical adapter)...whichever works best for your TV.

The second part is the speakers, the .1 is a Sub, and you can either use a Sonos sub or a wired sub connected to your amp.  The amp itself will power the front left and right channels with a phantom center...the 3 front channels.  The two remaining rear channels have a few options.  You can get a pair of Sonos speakers  for wireless.  Since you want to go cheap, the Sonos iKea speakers might be best option since they are $200 for a pair, and can handle surround duties.  Although, IMO, the Sonos One SLs are signifcantly better and on sale right now, at $260 for the pair.    If you want to use your own speakers, you would need a second amp.  The new amp would not need to be wired to the other amp (powering the front channels), but the previous model Connect:amp would need to be wired by ethernet.  Be careful buying used Connect:Amps right now, as some may be in ‘recycle mode’ and no longer functioning.  Others may be an older model that can’t be updated again after Sonos makes the change to S2 come June.

Thanks Danny - I ordered the HMDI to optical and the amp that I am using is a new version.  I really just wanted the five speakers to pass sound through while I was using the Roku for the TV.  It’s not an area we are in a lot - just no one likes listening to the TV through the actual tv :-)