owentdc,
From my experience owning 3 class D amps and those I've heard in others' systems, I believe they all have some common sonic characteristics: very good bass response, low noise floors, good dynamics, are highly detailed from top to bottom and and have an overall sound best described as neutral like 'a straight wire with gain'.
The neutrality of class D amps are beneficial since the sound imparted by the preamp, and the sound discrepancies between stock and swapped tubes, are usually easily discernible.due to the amps just faithfully amplifying the inputted signals without any audible sonic additions or subtractions.
The variances I've noticed between all of the class D amps I've heard is mainly with treble responses that typically are very detailed but also have ranged from smooth and almost tube-like to a bit overly bright.
Fortunately, I've perceived the treble of the 3 class D amps I've owned as detailed but still smooth and, on good recordings, there's even some tube-like euphonic sweetness I hear.
I've read some good reviews on your Wyred4 Sound STI-1000 but, apparently, you perceive some treble brightness.
I've actually perceived more treble brightness from my previous class AB amps (Adcom, McCormack and Aragon) than my subsequent class D amps.
I auditioned many good tube preamps searching for one to sweeten the treble on my high powered ss amps driving my Magnepan speakers.
This was about 1990 and I recall many tube preamps I tried in my system not sounding as warm and euphonic as I was hoping such as Audio Research, Cary and a few others.
The right solution for me turned out to be a VTL 2.5 tube preamp but I had to swap out the stock Russian or Chinese tubes for a set of 4 expensive ( $200 at the time) NOS Mullard tubes to get the warmth I wanted.
Currently, however, I've discovered my system sounds best for music and ht just connecting my main source, an Oppo-105, directly to 3 class D amps without using any preamp at all. The Oppo serves as a Blu-ray player, cd player, Dolby Digital 5.1 surround sound processor as well as a dac for streaming internet radio and NAS cd/hi-res files.
Sure, this configuration is typically dismissed by fellow A-gon members and others as sub-standard, but I don't mind a little ridicule since it's so streamlined and sounds so good to me. I also know some are just not aware of the high quality and versatility of the Oppo BDP-105
You may want to try this first if your sources allow before adding a tube preamp. If not, I'd suggest finding a good local dealer who'll let you try out some loaner tube preamps to audition at home in your system.
Tim
