Here's the deal with the Garcia version. At this point the only difference between the SMS Classic as a steel guitar preamp and a "Garcia" version guitar preamp is in the choice of treble capacitor.
For the super clean stuff like pedal steel guitar, I use a polystyrene or silver mica treble capacitor.
For the guitar or Garcia version, I use a specially chosen and "doped" ceramic disk. This sounds better for guitar and especially the Garcia tone. Ceramic disks vary. Some are glaringly harsh and painful to hear. Others are thin and grainy. But the right ones sound just like (or even better than) a vintage one as found in a '60's Fender. Ceramic is piezoelectric and the physical makeup, size, coating, and mass of the cap actually imparts tone character. This treble cap is critical too because it not only has high voltage on it making it exaggerate its character, but it also carries all the music above 800Hz or so. The entire high mid and treble band passes thru it. Anyway, after comparing and selecting and treating certain ceramic cap's, I got something very true to the original vintage version. For guitar, that subtle distortion and mild grit of a good ceramic disk just seems to put the right amount of hair on the tone. Not too perfectly clean as that actually can sound kind of sterile on guitar.
The other factor that contribute to the Garcia factor is the 3 plate resistors in the circuit. I had offered (and still do) either an earlier '70s version of the preamp using all NOS Allen Bradley 1W carbon comp resistors, and a more modern, cleaner version using the military spec 1W Dale metal film types instead. Now I'm using a combination of the 2, and that's what I like best. It seems to bring in the warmth of carbon comp, yet the low noise and bell-tone top end of the metal film. But whether a guitar/Garcia or a steel guitar version, I'm using the same resistors now for both.
Regarding power amps,
Last week I helped Dave Casper of Jakes Leg in St. Louis finish off a rig we'd been working on this past year. The final change was from his Boogie to a rack with the SMS Classic and a Fryette (was VHT) 2/90/2 all tube rack mount power amp. It was pretty amazing sounding. The power amp is very flexible tonally and just a clean tube monster. An ideal choice. There are some steel players who also use the steel preamp with that VHT/Fryette power amp. Only glowing reviews. The setup I'm eager to try is a McIntosh Mc2100 power amp to truly emulate the Garcia power amp peak limiter factor. Those can be found too. Carvin makes a more affordable rack tube power amp, and I'm waiting to get some opinions on that. I'd say if you know you play absolutely clean, then there are a number of nice sounding MOSFET amps like Hafler and Mosvalve. Stewart makes lightweight and clean amps. Boogie made a couple of nice rack tube power amps. If you think you're gonna lay into your guitar and drive an amp hard and into clipping, then consider a power amp that is tube or truly has some good limiting built in. Apparently, this limiting is something that helps make the McIntosh's so good for guitar, that ability to just bang on it.