One of the biggest areas that we've spent regarding sound quality has been the volume control method. There's quite a few ways to handle volume control and every one of them has some drawback. Some are inexpensive while some are quite involved -- and almost all of them sacrifice sound quality for cost/ease of implementation/reliability that are out there. This really plays into the lower levels that you won't read about in a magazine or see in a review, as many times they're playing it louder to focus on the sound. Many times we turn the volume down to listen to music more passively where a lot of volume control solutions struggle to maintain clarity.
As you've noticed, most preamplifiers provide a "house sound" of some type that may or may not be pleasant, but is almost never what I'd consider transparent -- which is what I personally believe a preamplifier should be. Different brands get closer or further from this and it's near impossible to audition everything out there to find what is right. I have opinions about our gear, of course, but I'm not posting to advertise.
Audio.bill is exactly right in the fact that EVERYTHING matters. The transformer is vital, the regulation that handles the voltage coming from the transformer makes huge differences. The components involved and the material that they're made out of makes a difference...we even found the material that the feet the unit rests on are made out of has an effect on the sound (which is immensely annoying when you start getting into that level of adjustment). Tubes vs. solid state, balanced vs. unbalanced, feedback vs. no feedback...they all play a major role. We obviously have our preferences at Ayre, and they all tend to be the hardest way to design and work with a circuit. I really wish easy and best would line up now and again, but rarely do they cross paths in our experience.
As far as measurements...they really tell so little about a product in this industry. Products that measure worse often sound better than products with fantastic measurements. Two products with nearly identical measurements sound completely different from each other. The measurements are great in the sense it at least gives you something to look at since you can't listen to them all, but ultimately they don't do much in how well you'll enjoy the product or what coloration it may be adding to the sound. Charley used to say the most important measurements you can get for a unit is the weight and size. That way you'll know if it'll fit on your shelf and if it can support the weight of the product. I tend to agree.
Best Regards,
Ryan Berry
Ayre Acoustics, Inc.