Okay. Enough is enough. The Marshall JMP-1 is a stellar unit. If you cannot get a usable tone out of it, you either aren't using it right, you don't have the right gear, or you have tin ears. So, assuming you're thinking about buying this thing, I will proceed to give you a decent user guide :
After you've purchased your Marshall JMP-1, find a good TUBE power amp. Some acceptable ones include VHT, Marshall, and Mesa/Boogie; the last choice being the best mate for this preamp. (I use a Mesa 50/50 but a 2:90 or any other class A or class A/B will work great; in fact 6L6 amps tend to sound thicker and bigger over EL34s)
Replace the old tubes with some new ones that are preferably matched.
Next, find yourself a decently built and assembled 4x12. Peavey makes some good cabinets, Mesa is decent, and so is Marshall. I was blessed and found a Crate 4x12 that sounds very very good. Don't know what it's made out of or what the speakers are, but it's HUGE.
Now, after you've hooked everything up, there's a button on the back of the JMP-1 under the Master that says "Level" with two push options "+4dB" or "-20dB". Select the "-20dB" (this puts less feed on the your preamp and as a result draws more horsepower from your power amp). Now, use the setting on your power amp that draws the most power from your tubes (on my Mesa 50/50 it's a simple Hi-pwr and Lo-pwr flip switch).
Turn your amp on, mess with your settings. If you want a huge, heavy rock/metal type of sound, push the Bass Boost button "ON" and then adjust the bass accordingly. After a few moments, you'll see what I mean and you'll abandon your computer to go play with your newly acquired rig.
If you follow these instructions I'm almost positive you won't be disappointed in this thing. There's a reason I say a 4x12 and there's an even bigger reason I say a quality tube power amp.
All of this should cost you roughly anywhere from $900-$1700 (including the JMP-1).
This thing has a habit of losing screws, washers, and knobs. I've seen many JMP-1's that have cosmetic defects and things missing... these units are not put together very firmly, but I would definitely trust it for gigs and studio use. What's a few missing washers?
If you can follow my instructions above, the JMP-1 more than likely will not disappoint you. I say this because I have played several amps and setups with numerous guitars and the only thing that comes close is Orange and they run at least $2k just for the head. Certain Strats will sound good through this (it really depends on how heavy it is and the phase of the pickups, weird I know) but the real shine is with humbuckers or over-wound single coils. Right now I'm using a Telecaster with a hot single coil bridge pickup and it gives me the crunch of a humbucker but the sparkle of a Tele. Les Pauls and SG's are good matches for this.
This amp has hundreds of possible settings if you look hard enough. The presence knob is a hidden gem that can completely shape the hollowness or the fullness of a tone, and the Bass Shift will get you instantly into metal territory if you are dialed in right. OD1 is a transparent, more JCM800 style distortion; while the OD2 adds another gain stage and gives off a nice furious fuzzy crunch.
All in all a good unit. The minor gripes I have about it are completely superseded by the excellence in tone.
God Bless, Jesus is Lord.