The first hit I got when googling VA transient:
and then there are several more, all connected to Naim. It is apparently not a standard audiophile or industry term, but I am no expert in amps. I think it is their way to quantify how good their amp is at handling the transient peaks. IMO the two qualities that set some amps above others is the ability to stay audibly distortion-free with a very fast response time (attack slope) and to the manage transient peaks (especially highly power-demanding bass) cleanly. Their VA term seems to apply to the latter.
I'll briefly summarize my limited experience of Dalis with some different amps in case it may be of value to you. I have my combo music/HT set-up in a16’X22’ family room with 8’ walls arching to / vaulted 12’ceiling (3500 cu’) family room, no formal acoustic treatments, natively producing lumpy bass FR. When I had the Heli 400s (the 2 way tower model a step down from Euphonis) as FR/L I first hooked them up to the internal amps in a Denon AVR4310 that I had at the time. hose amps were rated by Denon to operate 6 to 16 ohms. Though I wa running subs, the SQ audibly dropped off as I approached reference levels. This was easily solved by purchasing an Emotiva XPA5 external amp. It was cleaner and more dynamic at high volumes. That Emo amp has a reputation for being a quite good amp considering its "bargain" price <$1K (for ex., see Kal Rubinson's review in Stereophile).
When I replaced the 4310 with a 4311 for better DSP, I noted that the amps were rated by Denon down to 4 ohms so just for fun I once tested the FR/L Heli 400s in stereo (full range with no subs) vs the Emo. The 4311 did not poop out at volume like the 4310 and sounded pretty close to the Emo. BTW I kept the Emo in the system and returned to my usual practice running the speakers as "Small" with my high-quality Velodyne subs and sophisticated bass management in the AVR. I also use the Audyssey DSP room correction (Audyssey XT32 with Pro kit calibration) in the AVR as it tames the bass peaks and dips and overall improved SQ (again consistent with Kal's reports on XT32 and Pro) but that's not relevant to our conversation.
Then I replaced the Helis with Euphonia MS4s (basically the flagship 2 way tower model the Epi 6 replaces) and the SQ was significantly improved with the more precise speakers.
I then got MS5s and they sounded even better in the mids and lows, cleaner and more dynamic. I had the opprtunity to get a great deal on a used Halcro MC30 Class D amp (MSRP $5K and well respected in the HT community). The improvement in SQ is not huge but is distinct.
The Halcro is cleaner overall, and the transient response is very fast, producing a more detailed, dynamic and overall more life-like experience with the music. IMO that is what you should expect from a pricey audiophile amp driving your Epis.
googling Naim I stumbled onto this
thread mentioning a reference to some concern mentioned in a review in Stereophile mag.
And found this
nice but superficial review. As long as you can switch out models and brands of amps with the dealer, Naim seems worth a in-house demo.Edited by SoundofMind - 3/26/13 at 5:16am