On the bass response of each, as a stereo amp; Truly it isn't even close.---Then guess what?-- the rest of the spectrum is ALSO that much better. The 350a Ref is much quieter. I was never aware my 150Ref was noisy;when you compare the 2 it is one of the first things you notice. The treble brought out the Sophia's(2's) potential. This amp just does everything on a finer scale. The bass becomes the cornerstone of the music,clean and powerful.I seriously doubt 2 150's would have bass as clean and powerful.---Sure 2 150's may well have more bass than a single 150---BUT, amplifying X's2 doesn't improve the quality; only the quantity.----Oh yes, the improvement in the midrange matches the treble and the bass.Soundstage and depth of image---on the same improved level which is easily twice that of the 150. Everything is better, this is the whole package at a giant-killer price---used of course. Remember guys, this ain't a 6moons guy. This is from a guy whom ran the 150aRef for a year and then aquired a 350aRef.BTW, I also ran this 150 on Merlin MM's and sold them 'cause I didn't have enough bass---Well now I understand and it's called live and learn.