i have the head and it's an amazing amp. marshall
was trying to return to it's roots with this amp, but also retain some of the advances/improvements they've made over the years.
first of all though, it should be noted that a 50w tube amp is never going to sound good at bedroom levels unless you can reduce the wattage significantly. at volume level of 2, the gain is fizzy and thin, and it's already loud enough to piss off the neighbors. this amp doesn't start opening up until you get it to about 4 or 5 and then the tone warms up/thickens dramatically. that being said, i've gotten some decent tone at lower volume running my distortion/overdrive pedals on the high dynamic range setting (i.e., gain stage) with the 'body' and 'detail' knobs around 9'oclock. this setting is basically a very slightly dirty clean sound that you can use as your base tone to run your distortion pedals through. running a tubescreamer (and a bb xotic preamp pedal as for even higher gain) i got amazing tones from this amp.
imo, it really just boils down to your philosophy on amps and how you prefer to get your gain. if you are the type who wants the amp to provide all of your distortion, then this amp (and just about any of the older, one channel amps) is not for you. it is a one channel amp, with a footswitchable gain stage. so while you can switch between the low dynamic range (clean) and the high dynamic range (dirty), the low will always be much quieter than the high, which makes it ineffective unless you get some sort of booster pedal to run through it. ideally, you will choose one setting as your base tone (be it high or low) and build your tones around it via your pedals. while you will hear a lot of objections to this approach, keep in mind a LOT of pros are using this set up...including satch. even though the jsx has oodles of gain with it's 3 channels, he still prefers running his satchurator through the clean channel for his lead tone. i guess old habits are hard to break, lol.
anyway, if you are planning to run the jemini pedal through it, i think you will be happy with the amp. it may not have the most gain, but the inherent tone of the amp (and the overtones) are just heavenly. and if you are looking for gilbert's tone, this amp is a good place to start. although a lot of his tone really comes from his pick attack...