I have a 3400 and can say it's one of the very best purchases I've ever made. Have previously had Arcam, Linn, Naim and Meridian based systems, all of which were decent, but the Lyngdorf and RP are proving to be a revelation.
You do have to have the mic very steady to get the best results, so either get the stand built or do as I did and buy a better stand. My Studio Spares stand was around £12 delivered, so not a great expense and it is much better than the Lyngdorf supplied stand.
I've had the 2170 and 3400 on extended home trials and I found the 3400 better for my needs. I have heard the 1120 and it is a very good amp, but for a main system, I'd still take the 3400.
I should add that before Lyngdorf's RP system, I had tried Dirac (still actually have it on my Arcam AVR, but no longer use it), Audyssey and Anthem's ARC. RP has been the only room correction system that has worked for me on music and movies in my room and system.
Hope this helps.