hifiberry setup with AV originating at TV or at the Pi

Hi.

For the last 7 years I've been happily using Pi2 with HiFiBerry DAC+ RCA standard (HW 2.6) plugged into active speakers (they died) or more recently a Sony HiFi with amp and passive speakers. The AMP just died so I'm thinking about a new setup. 

I've been using the current setup mostly as a spotify client (https://github.com/dtcooper/raspotify). I could probably just buy Amp2, and still have the same functionality, however I'm thinking if I can upgrade what I can do with my Pi. Moreover, would Amp2 work with old Pi2? Would it be better to buy Pi5?

I'm thinking if I can pull off a setup where the pi also serves as a media streaming server - connected with HDMI to a TV for video, but audio would still go through hifiberry and the speakers. This seems fairly standard, I probably need just an Amp2 to make it work.

However if I wanted the TV to stream on it's own, would it be possible to have the TV's audio directed through the PI to hifiberry and connected speakers? It's just like the previous setup however audio and video originate on the TV rather than the Pi.

I can see how I can achieve that with an external amp with dual input, where one is the Pi and the other is the TV but I'm wondering if I can achieve that with a Pi and some HiFi berry goodness. It seems it all boils down to an amp with dual input, and I don' t see a solution for it without an external AMP. Did I miss something?

I'm not a HiFi enthusiast, more like a casual so I'd take any advice you might have. Thanks!