I was just here where you are: Krell MXC350 monos
purchased a pre-owned AR Ref5. Back to back comparison to the Krell HTS 7.1. Took some listening. The Wilson WP7 have had a hard, bright, edge to the high range. Ref 5 removed that edge. Some music was fatiguing and I could not put my finger on why. the highs now are humm buttery maybe, more musical, more organic less harsh. in any event the sound has improved although back to back was required. Bass however was a very pleasant surprise. The krell was muddy (dare I say that about krell) as compared. the Ref 5 brought a lot more punch and very good low hertz definition. Some tracks on Stanley Clark Bass Days no longer have a muddy thump but now have a very discernible pluck of the bass , not there before. Is the Ref5 a huge change, no, is it worth the dollar upgrade, to me yes ( my wife, no). However I can now listen without the fatigue and that makes it worth the investment to me. I agree with the previous post, a bought a 20 % improvement