How much do I need to spend to get a preamp that sounds better than no preamp?

George , I tried to PM you, w/o success. If you could PM me, that would be great. I have had a few passives, but none were exceptional. The particular room and system I would be using it in would be : CD, mostly redbook, modified Sony SACD player, into a modified Adcom GDA 700 D/A converter, into a Nuforce STA 200 amp. I might use my modified Klipsch Lascalas, but have a pair of modified Heresy IIs, with some subs. I believe the Adcom into the Nuforce would be " ideal " together. Enjoy, MrD.

all I could find on the Baxandall was math and schematics. What good is that?

Pretty good if you want one and no-one sells one. You just have to find someone to make it. We can do stuff like that, but as a one-off it might not look at that great.

It has a lot more VC control, in addition to a significantly reduced noise floor and a much bigger sound stage. I was surprised by how much bass was missing from the 105 direct to amps.

Yup. The difference between passive and active right there.

George , I tried to PM you, w/o success. If you could PM me,

Done.
Looked it all up, and your right to go for the Lightspeed in this system. 
Your Adcom with 78ohm output impedance at 2.1v is a perfect match.
Your Nuforce at 51kohm input impedance with 0.45v input sensitivity for full output, is also perfect.

As you can see you only need 0.45v into your amp to give it's full wattage output, and you have 2.1v from your source, so you don't need an active preamp adding more gain.

Remember what Nelson Pass said.

Nelson Pass,

We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.

Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

    Cheers George