What Muiltichannel amp for Dali 800 MKII

I wouldn't downgrade Pass X350 to a multi channel amp. While I was setting up my multi channel audio system I went through several highly rated single box five channel amps from Theta, Proceed and EAD. While they were pretty good in performance, they all lacked the ultimate refinement and resolution that you find in high end two channel amps. I am now convinced that multi channel set up should be organically grown from solid two channel set up, rather than built using dedicated multi channel gear, in order to sound best. I would get the best two channel amp for fronts, then add three channel amp for center and surrounds. Pass X3 would be a good complement for your X350.

Ultimately it's about the trade off and priorities. Five identical amps all around will make it easier to tonally balance all the channels. 2+3 may be trickier to set up, but it will be superior in two channel music play back.

You should note that even with five identical amps, unless your speakers are also identical you won't automatically get tonally balanced set up. You'll notice the imbalance immediately when you play white noise on each channels if your center speaker is not identical to LR fronts. You'll most likely need to adjust the gain for each channels. If you have room EQ on your processor it would help with the imbalance.

Having said that, X3 and X350 will have more similarity than difference. I have never felt that I needed more power when I was drivng B&W 804 Nautilus speakers with X3. YMMV.