Ah yes, the rack system. I am a gear slut and I'm not ashamed to admit it.
This is just the main business end, the conventional guitar amp rack. At the top I have an old Alesis Quadraverb, bypassed about 90% of the time but useful for things like tempo-matched delay times and for putting the occasional Pink Floydy "halo" around a lead guitar line.
Under that is the main preamp, an ancient ACT MP100T dating from around 1990, a MIDI-enabled valve unit with fully programmable overdrive, compression, pre and post distortion EQ sections, FX send/return levels and a very useful MIDI program change mapper that I used to use to map effects changes on the Quadraverb (these days I use a MIDI thru box instead so the ACT and the Quadraverb both receive the same patch numbers). The sound from the ACT is unbelievable, lovely Fender Bassman style compressed twang and crunch and some very nice overdive tones. It doesn't quite reach the same levels of insane distortion as my old Marshall 9001 preamp but that's not really my style.
The power amp is a dual monoblock Marshall EL34 5050, pretty much the industry standard for a guitar rack system and a vast improvement on the Marshall 9040 transistor power amp I was using before. The overall sound of this setup is beyond belief, like a programmable Fender Bassman with a Marshall power amp. The Quadraverb is in a parallel effects loop so the signal path really is all valve from input to output. Speakers are teo Marshall 1912 cabs with Celestion drivers.
I like my synths too - the other rack contains a Roland GI-20 guitar to MIDI convertor connected to a Roland JV1010, a bit dated now but it certainly expands the range of tones I can pull out of a guitar. For now the JV is running through my old Marshall 9040 power amp into a Marshall 1936 stereo cab and both racks can be switched from my Roland FC-100 foot pedal unit.
My most recent aquisition is a Roland VG-8 virtual guitar processor which uses the same hexaphonic GK-2A pickup as the GI-20 guitar synth. At the moment this involves unplugging the GI-20 and plugging into the VG-8 as Roland have unhelpfully discontinued their GK series A/B box so I'll have to get the soldering iron out and cobble together my own A/B box sometime soon. I'm also looking at using the VG-8 pedalboard instead of the FC-100 to control all the MIDI, with the added advantage that my expression pedal can be routed from the VG into the Quadraverb and the JV1010. While I'm at it, I also want to build a rackmount mixer using valves to sum the JV1010 and VG-8 into the power amp.
Update 27/03 - I got tired of the Marshall cooking the preamp for hours so the current setup is:
Rack 1 - Preamp, MIDI and Effects
Roland GI-20 guitar to MIDI convertor
Roland JV-1010 synth module
Rack 2 - Marshall Power Amps
Marshall 9040 power amp (200 Watt a side stereo MOSFET)
Marshall 9100 power amp (50 Watt a side dual monoblock valve amp)
And the pedalboard is just overkill but I know how to tapdance across it:
UPDATE: The rather elderly Quadraverb has now been replaced with a swanky new Lexicon.