For the millionth time...

[earthtonesaudio]

I second Hides-His-Eyes' suggestion of a passive attenuator.  Set your "quiet" level and then bypass the attenuation to get your "boost".

[Mark Hammer]

Correct me if I am wrong, but I think the idea isn't to magically surpass the amps headroom, but a pedal that itself will color the sound as little as possible. The amp will always be your upper limit on amount of headroom available, but I think the idea here is that you don't want a pedal to be your limiting factor.

Correct, but in most cases, the puniest and simplest of single-transistor gain stages will generally exceed the amp's headroom.  Cripes, in many instances, even in the total absence of cascaded gain stages, a power chord from an SC-equipped guitar, fed in directly, will exceed the headroom of the amp.  Why anyone would expect doing gymnastics to extract clean 15 and 20db gain from a pedal would result in a clean amp sound is beyond me.

There is every reason to expect that a simple gain stage with modest boost (and sufficient supply voltage to support that objective), feeding an amp NOT set at the precipice of distortion, can produce a pleasing increase in level for solos without any coloration.  There is no reason to expect a gain stage that uses a 48V supply, and an astounding array of state-of-the-art "audiophile" MOSFets, to produce 20db of gain, to be able to produce a clean boost with the output of that stage set more than just a modest bit above unity.

Here is yet another case where folks can easily ignore context.  If you want to run a voice mic into your amp or through a guitar effects pedal, do you need to boost the level of the mic signal?  You betcha.....a LOT.  Does the power supply and overall design matter, when it comes to achieving that gain cleanly?  Sure.  Does all of that apply to running a guitar signal into an amp?  Not really, unless you're feeding a guitar into the line in on a power amp.

[Govmnt_Lacky]

Spoke with him today. Apparently, he already has a passive attenuator but he did not use it because it was an in-line attenuator that was always on.

I told him to let me have a look and I would probably be able to install an on/off stomp.... possibly an on/off LED. (depending on room. He said it was a small box)

So this is a possible PROBLEM SOLVED 

If not, I will probably dive into a circuit on the breadboard and see what I can get 

[thedefog]

Attenuate...... No 

Amplify/Boost...... Yes 

The amp has a limit. There's nothing you can do to the pedal itself to give the amp more headroom.

Give him a compressor and trick his ears?

But this one goes to 11