I certainly can't argue at all about the best location of the unit & air return, everything mentioned makes sense to me. The experts/ professionals such as SierraMikeBravo have studied and tested way more about this than I could ever imagine.
Given I did do a min-split with the in-room unit/air handler, I am happy with the location of my unit and wouldn't change it despite, the apparently sub-optimal functional location. This is entirely based on the aesthetics of the in-room air handler and how trying to fit it closer to the front of my room would look. One of the benefits of the ducted mini-splits or conventional forced air systems, is you don't have the same aesthetic concern as with my kind of Mini-Split. If I were to do it again, I would learn more about the ducted Min-split option.
In terms of the 'sound proofing' compromise, I don't find it to be a big deal. The entire penetration in my room shell for the on wall unit, is a circle, I would guess is 2" in diameter (insulated copper tube & electric wire). In that immediate area, I added an extra layer of DW between the studs & placed extra insulation around it, and it doesn't seem to leak sound much.
In general, I strived for 'quite good', not 'perfect' in my theater. I unequivocally know that if I had Erksine Group designed my theater/ acoustic treatments/ av system, it would have delivered a better total performance...but, I am not an audiophile or video-phile, so, for my personal needs... what I have is fantastic in my opinion (and in the opinions of others who have visited the room, all of whom are also not true audio/video experts). I had a higher end realtor in my home recently, who said she has sold ~50-100 homes with dedicated home theaters... and she said "wow, this is really nice, is this what you do for a living?"... so, I took that as a compliment :-) Having said that, the entirety of my Home Theater knowledge is from reading largely on this site, so, quite limited vs any professional. I am just sharing a perspective of someone who strived for quite good, not perfection... not everyone is willing to spend the extra money to go from quite good to perfection.. I like to think I got 80+% of the benefit for 20-30% of the effort/cost. Naivety and ignorance of how good, good can really be, is nice sometimes :-)