It may be that the other receivers have more gain on the controls than the 2150. I would expect that you would get better performance from any setup using a sub to do the low freq stuff. Even bass capable speakers like the Klipsch can benefit because of the additional headroom available when the sub takes on the heavy stuff. I suspect that when Outlaw designed the 2150 they had the use of a sub in mind with a set of bookshelf speakers and didn't expect someone to crank the tone controls all the way up to get as much bass as you want.