"honestly the signal from my two front channels will mostly be absorbed by the couch"
No this won't compute much here. Bass modes will still abound, even with the largest of couch and furniture infront of the speakers, regardless of what speakers the bass is coming from. The room modes will still excite, and be audible.
"open ended on three corners I doubt the room modes will be that severe"
Doubt? Yeah, if you get in there an measure (and listen) through the frequency sweeps, you'll be able to tell where you're at--which is the only way to tell. Yes, possibly, depending on seating arangmenents, you may or may not be able to get away with good fidelity and smooth response, in some possitions. But you gotta measure and test to find out, yes.
I've not seen the room, but Know from experience what usually ends up is modal problems at certain points, regardless of how open the room is. I hope it works out very well for you however.
I recently did a lawyers home theater in the main living room, that was open on both sides of the listening space, and the room was 21feet deep x over 33 feet wide (43 in once spot)to the open spaces, with a 10-11 foot tiered/coffered ceiling. After running through all the test frequencies, and test material, the owner strongly concured that we needed another pre/pro in his system--one that had a parametric EQ built in, at the time. Problems solved, the 3 main bass mode problems were eliminated (over 20db boost at two frequencies!!!!!...bombastic to say the least!!!!...not hi-fidelity).
Anyway, it's always a consideration. Nonetheless, I do hope you get better results with your Arcam option, if you go that route
