Hello jz,
I have a bit of history with Ascent i, Krell 400xi, and Sunfire. If you do a search of my moniker you'll see a few threads with pertinent info.
But since I'm here - I had Magnepans that I drove with a Sunfire Stereo II amp / Quicksilver preamp. The Stereo II put out 650 watts into the 4-ohm Maggies; not sure how it compares to your Sunfire but I believe the technology is similar (i.e.: Tracking Downconverter power supply). I liked the combo a lot.
Then I got a 400xi with the Maggies. The sound was very different, and I'd say that some would prefer the Sunfire, some would prefer the Krell. I preferred the Krell. The Krell provided a lot more detail and really controlled the Maggies well.
I then switched to the Ascent i. I wasn't familiar with the ML sound, and the Krell/ML combo sounded pretty good and improved as I made changes. I pulled the Sunfire and Quicksilver out of the closet to take pictures to sell them, and hooked them up for kicks. Big difference. The Sunfire mated with the Logans much better than the Krell. I don't think it was a matter of personal preference at this point (like I believe it was with the amps and the Maggies). The Krell sounded very thin to me, and just didn't seem to work the panels like the Sunfire. I sold the Krell and kept the Sunfire / Quickie.
After a while I went shopping for another amp and stumbled onto a dealer demo Primare 75 wpc integrated ($1500 MSRP I got for $1000). I wasn’t expecting much, but it really impressed me. I do have a small room (12’ x 13’ x 9’ high), so 75 watts might not do in a larger room. I ended up buying it and the matching CD player.
So, my experience is that the 400xi is a very good amp but does not match well with the Ascent i. I believe a little searching for other integrateds would pay off.
Good luck, and hope this helps,
Mike