In the film "Psychedelic Sexfunk Live from Heaven," John Frusciante is shown using a Mesa/Boogie Quad Preamp. This is supported by a photo from Daisuke Hirata on Flickr.

“The The live amplification is a racked set up based around two Boogie Quad preamps, a Boogie 295 poweramp, and a tc 2290. The tc's effects loop takes in a Yamaha GEP50, Roland GP8 and Korg A3 guitar processors, an Eventide H300 Harmoniser and a tc spatial expander. Speakers are two Marshall 2x12" cabs loaded with EVs, and the whole set-up is doubled for live work in case of breakdowns.“

At 5:04, John Petrucci and Doug West reveal that in the album "Images and Words", John used a Mesa Boogie Quad Preamp

In 1989/90 Squire had firmly grounded his liking of mesa boogie amplification. This was a company who were arguably leading the field in valve amp technology. Squire had ditched the limitations of the twin reverbs and wanted to immerse himself in the more versatile mesa boogie tone. Having used a Mesa combo for the past few years. Squire decided to rack mount his set up with even more versatility. Mesa Boogie had released a rack pre-amp called the 'Quad'. This encompassed almost all the tones available from mesa amps. It had rhythm and lead channels of the Mark II and Mark III amps built into one.

In this Instagram post showcasing Fredrik Thordendal’s rack, you can see a Mesa Boogie Quad Preamp just underneath a Fractal Axe-Fx unit.

"With Tin Machine I was using a Steinberger through a Mesa Boogie Quad Preamp and the Boogie Simul-Class Stereo 295 power amp and two 4x12s."

Huff has been known to use a wide variety of equipment. Within the Tyler brand he has been known to use the Tyler Classic Signature Model and the Tyler Ultimate Weapon with active mid-boost circuitry, a recessed Floyd Rose Locking Tremolo and dual humbuckers that give off a “warm fat sound.” (James Tyler himself has described it as “a sort of Les Paul-meets-Telecaster.”)

For his other acoustic/electric guitars, Huff uses a range of Stratocasters and Telecasters, a Tom Anderson Classic T, and Gibson Les Pauls. When it comes to amps and effects, Huff has more gear than most mortals. Some of the featured gear from the Giant days includes:

Peavey 5150 Mesa/Boogie Quad preamp with VHT stereo tube power amp Mesa/Boogie Mark II TC Electronic 2290 Yamaha SPX90 Roland SDE3000

Spotted in Rolf's rack case.

According to this gear photo, which is found under Denander's gear photos, one of the units is the Mesa Boogie Quad Preamp.

The Quad Preamp can be seen in the rack below the IIC+.

Sisters of Mercy gear list, circa 1991:

Tim Bricheno Squire Strat, 2x Squire Tele, Gibson 'Chet Atkins', 2xJC120, 2x4x12 Marshall cabs, 1x50w Marshall amp, Ibanez Tube Screamer, 2xBoss DD-3, Boss MZ-2 Andreas Bruhn 2xKramer Focus 1000 (with DiMarzio PAFs), Mesa Boogie Strategy 400, Mesa Boogie Quad pre-amp, 2xMarshall stero cabs, Quadraverb FX, Rat distortion, Morley wah-wah, Boss CS-3 Tony James WAL Custom bass, WAL MIDI Custom bass, 2xAMPEG SVT amps, 2xAMPEG 8x10 cabs, Korg A3FX Sequencing Compac 386 portable PC, running Voyetra software, 2xAkai S1000, with external hard drives