I'm currently running a 5.1.2 system, all from a denon X3700H. The main front left and front right analogue pre-outs (so forget the subwoofers) go to a miniDSP 2x4HD anologue inputs, doing PEQ and XO all IIR, with the 4 outputs feeding a 4 channel amplifier to power highs and midbasses of the front left and right speakers (no passive XOs). This works pretty well with only IIRC ~5ms delay.
So I would need 2 analogue inputs and 4 analogue outputs. Was hoping to play around with more DSP options as I have a pi 4 here already.
Thanks for the reply Michael. Looks like I might stay status quo to avoid the audio delay. (About to start up my rant about TV manufacturers not including video delay, how hard would that be... grumble grumble)