My Amp:   I stole an idea from a good friend of mine, Tom Mooney (of 'Mooney Steel Guitars', Memphis Tennessee ) and decided to cut down my Peavey Session 400; and use it as you would a Tube or Pro-Fex, close to the steel.  On removing the amp from the cabinet, I discovered the underside was perfectly flat, thus making it ideal for fixing 19" units to.  As you can see from the picture, I've added an Alesis Digital Reverb and a Peavey all tube pre-amp, which I prefer to use when playing guitar.  I originally used the amp with just a single speaker cabinets (Due to all the dire warnings I'd received about trying to use two).  It would have been possible to have had two speaker cabs. and still preserve the 4 Ohm impedance, by using two 8 Ohm speakers.  But Peavey don't make these 'voiced' for guitar use.  However, I recently took the plunge and started driving it through TWO 4 Ohm cabinets (and thus into only a 2 Ohm load), and it works fine!
John Le May Modification Kit:   A while back, a friend of mine recently returned from Canada, singing the praises of a modification kit for Peavey Amps.  These Kits are made by John Le May (Of Miracle Audio Products).  The good news is that he brought one back for me.  (At a cost of £70).  John Le May provides kits for Session 400's, Nashville 400's, Nashville 500's, Pro-Flex, Vegas and so on.  The mod. comprises a handful of chips, capacitors and resistors.  But be warned: the tracking on the Session 400 circuit board is extremely fragile and you need to be mega-careful with the soldering or you'll destroy it!  I'd recommend you get a professional to install the kit.  (I was lucky, and had my brother do mine for me).  The mod. does everything it claims to do in the ads. ..(and More!!! ).  It's brilliant:  The string separation is greatly enhanced, the 'muddy tones' of the lower strings are gone, the overall sound is cleaner, brighter, 'tighter' and also considerably louder!  I don't think there are any plans to market the kits in the UK just yet, but there is a Le May web-site, so perhaps you could contact him and arrange to import a kit.