Using 2 EQ Pedals and a Power Attenuator with an Amp or Processor
>>How can I get better tone using my guitar preamp/processor and tube amp?
Bracket the preamp/processor, especially the distortion stage, with eq pedals, and experiment. The easiest eq pedal to use is the Boss ge-7, and the cheapest is the Danelectro $40 one, which I haven't heard. Try cutting bass or boosting mids before distortion -- depends on which pickup selection you use.
You can also try just the amp, but bracket the amp's preamp distortion by eq pedals. Once you find good tone that way, add the other gear and turn off amp's preamp distortion and move the eq pedals around the first part of the guitar preamp/processor to emulate the amp's built-in preamp distortion.
For researching tone and studying your gear, use what I advocate as the standard way to use a tube amp:
amp's built-in preamp distortion
eq pedal in the amp's fx loop
amp's tube power amp
good power attenuator (Hot Plate, set to at least 12 o'clock on right-hand knob; played loud in concert to push the speaker, to get speaker smoothing & spk dist.)
After using that modestly augmented straight-into-amp setup at home, you then can try removing the auxiliary gear (eq and power attenuator) and using a preamp/processsor before the amp.
I find pre-distortion EQ to make a huge difference, even from one guitar to another (they all sound very different in character) and generally, I'll always use that. But after the preamp distortion, I only need a little eq; the amp's tone stack is sufficient. So if I could only use 1 eq pedal, I'd put it before any preamp distortion.
That's about the only advice I have, short of fully detailing your system, but I think it is the most basic and helpful advice.
My advice about a tube amp assumed a traditional tube guitar amp; it doesn't apply to a rack-mount tube power amp that has no built-in preamp distortion.
The only way you can bracket preamp distortion by eq's if you have just a preamp/processor and a pure power amp, is around the front part of the preamp/processor (assuming it's a traditional type of preamp/processor).
The basic idea is that, wherever the preamp distortion is generated, whether in a pedal, in the front part of a guitar preamp/processor, or in the front part of a traditional tube amp, bracket it by eq's; put one eq before that distortion stage and one after.
One of the most desirable features in a preamp/processor is an fx loop between the preamp distortion and the time-based processing; you can insert a post-distortion eq here. After you quickly dial in a good eq curve, you can then slowly program that curve into the preamp/processor, and then possibly remove the eq pedal.
Every guitarist ought to be told about eq>dist>eq the first time they pick up a guitar. The BOSS pedal booklet shows this.
Today's floor processors aren't the best design. I went to pedals because I realized I myself am more interested in ease of dialing in sounds, than in programmatically storing them. For tone research, the complicated processors only got in the way. There is a reason why there's been a huge resurgence onstage of traditional tube amps and pedals (and, a choice to limit the range of one's concert tones). Floor processors in principle have potential, but I'd design them differently.
I've heard some impressive sounds from floor processors driving a traditional tube amp at modest levels. There's potential there.
I wonder if you're using too many watts of amp, driving too many watts of guitar speakers. I'd try using only one side of a rackmount tube power amp, with a good power attenuator, pushing that side of the amp into moderate distortion. I'd try using as few guitar speakers as possible, and pushing them very hard. -- rather than running the amp and the speaker in their linear, undistorted range.
The goal is to, at the desired resulting volume level in the room, get some power tube distortion and some speaker distortion, as opposed to not having any power tube distortion and not having any speaker distortion at that volume in the room.
When I've heard floor processors sound good with a tube amp, I suppose that was with a less than a 50 watt amp, driving a single guitar speaker.