The AVA FET Valve CF is a nice clean preamp that will reveal all the nuance in recorded material. The preamp is completely quiet. My system is used for both stereo and home theater, in home theater mode the preamp's volume knob line is set at 12 noon to match the other amps in the surround setup. At that high volume there is no background noise from the L & R speakers, no hiss, no hum.
Sound emerges from a black background with center images that are solid and float in space. Bass is deep and tight without a hint of tubyness.
The FET Valve CF preamp pairs beautifully with the AVA Vision SET 400 amp which is very slightly on the warm side of neutral. Paired with revealing speakers like my Salk HT2-TL speakers the results are magical. Interconnect cables do make a difference. The Straight Wire Encore II is neutral, affordable and works well with AVA electronics, at that price nothing compares (check eBay). The next level of cable that takes the system from 'great' to 'wow' is the Zenwave D3 interconnect. I can wait a year before a used pair shows up for sale and then I have to jump because it will be sold in an hour.
I still use the stock JJ tubes. At one time I checked the price of NOS tubes mentioned in the review and they were too rich for my blood, too bad you can't try before you buy. Tubes that sound great in one system can sound lumpy in another.
No background noise, no hiss or hum is all key points to my system. I can't have any of that. That kind of noise ruins my listening experience. Sound coming from a black background is important. I am using a nice passive pre right now with manual volume control just for those reasons. It's dead silent.
You touched on another key subject, I am an image fanatic. The sound, if meant by the artist, needs to be front and center, not a little off to the right or left. Why having a balance control was a must for me. I have monoblock Alan Eaton 45 SET amps that have volume control, so I can dial in that center image by turning up of down one of the amps, but my monoblock Class D amps do not have volume control so making sure I had flexibility with adjustment of left and right channels was important.
In regards to the SET 400, it's been on my wish list for some time now. I have GREAT amps right now but really want to give this one a go. I am sure with my ZU Audio's, it will make them sing!