TV HDMI to receiver plus optical to Amazon DAC to sub? You wouldn't have the ability to set crossovers or do room correction but the sub's controls would serve their purpose. That's if your tv can do both outputs, of course, and it's highly likely your AVR has a sub output already.
Or do you mean TV speakers plus optical DAC?
I probably need to elaborate on this a bit.
I currently use a minidsp SHD with a pair of Genelec 8341's. The 8341's have an aes/ebu input. I was thinking, if I bought a "digital only" DAC, could I utilise one if the digital outputs to feed my analogue powered subs via this little device?
I could then use a true AES/ebu output to my 8341's.
I hope that makes sense!
Please don't ask why I'm considering any changes though as I'm a bit of a tinkerer so like to swap my gear around every now and then!