What comes to mind is a Barber 'Launch Pad'.
I do not yet own one, but according to Harmony Central, they seem to be described as more silent that the Zvex 'Super Hard on' which I first considered.
I also like the idea of a larger casing, separate + and - phase out - and the idea of it internally converting the 9v supply to 18volts to give more headroom within which to work.
I see they have some in stock at 'strings direct'.
Also, on : forum.TPNgear.com
There is an interesting article in the 'Barber Shop' section( written by David Barber himself ) - about gain staging and "amp cooking".
I however would be using it on a clean amp to get more of the same but lifted by a few dB.
Regards,
F.F.