The cleans are great, after all it is a Fender circuit. The overall tone can be changed by changing tube types. EL34, 6L6, 6CA7, 6V6. There's one for sale at Steam music in Topeka. http://www.steammusic.com/[/url]
I have a Reissue Mark I. I tried el34's in it and the woofy bass was much better. Try turning up the master volume first, then the ch1 andch2 volumes. This gives you more power tube tone and less preamp tube tone.
I recently bought a 2001 mark I reissue. If the one you are looking at has mods, listen to it first. If you like the sound buy it. It's more like the originals than the first reissues. The bass is woofy if turned past 1. It can sound close to a MArshall but it's not a MArshall it's a Mesa and...
Here's a nice trick. If you plug a hotplate into the other speaker out and set it to load, it will not color the sound at all. The amp will see 2 speakers but only the real speaker will work.