Among the 4 or 5 amps I've owned in recent years, my most recent included the BAT VK-500 w/BATPACK, then the SimAudio Moon W-5, and then the McCormack DNA-2 LAE (Limited Anniversary Edition).
The VK-500 had a powerful and contolling lower bass region, but the mids and highs were just kinda' there. Subdued with a lack of bloom in the mids and lack of air in the highs as well as possible rolling off. Overall, pretty dark and flat. In comparison, the Moon W-5 had a fast, open and airy, articulate, and somewhat sweet mids and highs (excellent in this area), but the lower bass regions just were not enough for my Aerial Acoustic 10T's.
Listening to the W-5 after the VK-500 was like flipping on a light switch. The W-5 was very detailed and transparent in the upper regions compared to the darker presentation of the VK-500.
Installing the McCormack DNA-2 LAE was like combining the very best attributes of the BAT VK-500 and the Moon W-5, only faster and more powerful than either of the previous two amps.
Only thing missing with the DNA-2 LAE was that certain little bit of sweetness (possibly a coloration but nice nonetheless) that the Moon W-5 presented.
For me, I wouldn't even consider a Levinson or Krell. Especially for what they charge.
-IMO