I know you have subs, BUT, they need to take the low bass out of the line level, then back to amp, some do, some don't.
Some give the speaker's a break, but not the amp. Some give the amp a break which gives the speakers a break.
With borderline power for 'not too efficient' speakers, you want to give the amp a break, so it has plenty of power when not trying to create low bass.
Subs self powered?
front firing?
Fit next to where mains will go?
That will give you Stereo Bass, a wonderful thing, at any volume.