Krell 400xi vs NAD M3 vs Music Fidelity A5 vs Naim

With those budget, the Naim doesn't suit that and you should replace with Supernait instead of Nait5i. Then, it will be fair....

Those were all on my short list.
Krell 400Xi - the one I went with. It has a Krell house sound that at first sounded overly forward but I grew to like it quite a bit and became a Krell convert. Very detailed and open soundstage. Clearly separates the instruments. Feels strong across the board and sounds great at low volumes.
Bryston - didn't hear one but have heard a number of people say the Brystons are lively and have a dull, leaden sound. I think they get a good rep because of the 30 year warranty or whatever it was they used to carry.
NAD M3 - had NAD separates and they are a step down from, say in every way from, say, the Krell. Looked at the M3 and it looked cheaply built on the face and all. The top of line NAD separates were also cheaply built hardware-wise. Good sound for the money I guess. Lows ok but not particularly detailed. Also didn't have the gas to drive my Aerials.
MF - Personally, I don't care for the MF house sound. It has a kind of false warmness or presence that take the detail out of the music. I think a lot of people like MF because it hides the harshness you hear on a lot of systems.
Naim 5i - Great sounding little amp. Nothing like their high-end stuff but very nice. Underpowered for anything but efficient speakers or an office or bedroom system IMO.

regards, David

Save yourself some loot and get a Plinius 8150 or the 8200. I bought an 8150 as a quick fix because my main system is in storage. I was absolutely stunned. Musically the 8150 beats my Pass X-250 in my A system. I'm using the 8150 with a pair of mini monitor PSB B-25's. I'll match this sound with any amp/speaker combo for under 1K under the sun.