This all said...There's a late 70's 100w JMP at that studio, according to their website. If it's a nice one, and you're going for that Les Paul/Marshall Slash sort of a sound, it will most likely be nicer than the DSL. Those JMPs were basically JCM800 circuits before the JCM800 came out, and they can be extremely good. The transformers are better sounding than anything available to Marshall today. But it might not be such a great one...A lot of those things have been heavily messed around with over the years. Try it.
I'd also advise you to try separating your sounds a little between the two of you. You can try the AC30 for the other guitar perhaps. OR try the JMP on one and the DSL on the other. Maybe one guitar slightly lower gain.
Ultimately you need to work with your engineer to get a sound that YOU like. Make a choice on the day and stick with it.
You can not change the sounds you record very much. You can bring out a bit of midrange or clean up the bottom end but ultimately what you hear when you track is more or less what you will hear on your record. Don't imagine that it will change much. If you're not hearing something you like when the red light goes on, stop and work on it. There's nothing wrong with spending far more time working on getting a sound than on actually recording it if you're good players.