Lyngdorf TDAI 2170 vs 3400

I have not heard either unit (no dealers within my vicinity). I was intrigued by the reviews and the room correction potential.
What I have auditioned is listed below in order of my preference.
Luxman 550 AXII
Luxman 505 UXII
Naim Supernait 3
Anthem STR (room correction was not engaged, amp sounded very flat)

Aside from the above, I am also interested in a used Pass Integrated or Mark Levinson 585 (this may be a topic for another forum inquiry though!).

I own the Lyngdorf 3400 and have heard the 2170.

If you don't need a streamer/Roon endpoint, internet radio and more power. Go for the 2170, it has slightly better sound (I think, haven't done A/B comparison).
Yes, Bjeiesen is right. The praise for Lyngdorf on this website is over the top, but they are not that bad.
For $5500, you get DAC, integrated amp, room correction, streamer with the 3400.
You would be hard-pressed to find a system at $5500 (new price) that would beat the SQ of Lyngdorf and do everything it does. You would have to spend 8-10K (new price).

But that also depends on what you listen to. Rock, pop, jazz is not bad, but instrumental you might want to put some tubes before the speakers which is what I do. Lyngdorf 3400 connected to a tube amp to the speakers sounds quite amazing.

Also depends on your room, if you really need room correction go with lyngdorf it is a no-brainer, if not, you can look around. 

In the end like anything it all depends on your priorities, budget, music you listen to, need for RC, and convenience.

Lyngdorf with its app and remote is insanely convenient and can be left on all the time, which equals more music listening time.

I know you said it was not an a/b comparison with the 2 units but was it on the same speakers in the same room at different times? What speakers are you using? Thanks

I have the 2170 in my second system.  It was an ideal solution for me, because the second system is in a room with terrible acoustics.  The 2170 displaced a pair of highly regarded Coincident Frankenstein 300B amps.   The 2170 performs better in that room because of the Room Perfect correction.   Don't get me wrong.  the 2170 is not better than the Frankenstein in absolute terms, but in a room with problematic acoustics where room treatments are not an option, it can be a very nice piece.  Doesn't sound like a tube amp, doesn't sound like SS, and certainly doesn't sound like what I would have expected for a class D amp.   As for how it compares with the 3400, I have no direct experience.  But I have heard from others the 2170 is preferred based on sound quality.

Yes, same room, same speakers. My speakers are Devore Orangutans O/96 (not the best match for a class D amp, this speaker likes tubes).

I cannot honestly say 2170 was better. My 3400 was disappointing for the more than the 6-8 months until it fully burnt it, it takes a long long time. The 2170 was a demo unit of a dealer so must have been fully burnt in.

Perhaps if I try the 2170 now, the SQ might be similar.

This amp takes a long long long time to burn in, so take negative reports of new users with a pinch of salt.