I went through the same thing your going through. Bought my RM100 and thought that it sounded pretty shitty for a tube head and was contiplating selling it as well. First thing I found out was that my power tubes were biased cold and at all different levels. All you have to do is go to Radio Shack and buy a cheap digital multimeter, they are like $15.00 or so. Turn the amp on and let the tubes warm up. Make sure all your volume levels are all down to zero on the modules and master and then flip the standby switch into play mode. Put your multimeter on the 2 DC setting and then insert the black test lead on the multimeter into the "common" ground input on the back of the amp. Each tube has a test point so check them one at a time inserting the red test lead into each test point. Take a small flat head screwdriver and adjust the bias setting at the bias adjust. Turn it left to lower the bias and right to raise the bias. You will need to find out what type of power tubes you are running in your head to know what to bias them at. I would imagine you either have 6L6's, EL34's, or E34L's. You can bias the 6L6's or EL34's at 38 millivolts. If it is running E34L's I would bias them at 45. I originally had JJ E34L's in mine and switched over to Groove Tube 6L6 GE's. I think they sound better and have better low end. I run them at 38mv. I would use all 4 power tubes. I think it sounds better and you can get plenty of distortion at low volumes. After adjusting my bias settings it made a HUGE difference.
The next thing I would check on the amp is your common input tube. If you look inside the amp head you will see 3 small aluminum cylinders on the left side. These are just covers and inside are 3 preamp tubes. The 2 in the back run your effects loop and the 1 towards the front is your common input tube. When you run a module the signal passes through this common tube first and then to your module so essentially you run 3 preamp tubes per channel......the common input tube and then the 2 preamp tubes in each module. When I first started messing around with switching out preamp tubes in my modules I bought some JJ High Gain ECC83S's. These made my amp sound dull and did not do much in the gain department so I replaced all my preamp tubes in my high gain modules to Electo Harmonix 12AX7's. This helped out alot and gave me more gain but I felt that it was still missing something. Then I read the RM100 manual and found out about the common input tube so I checked that and what do ya know, another JJ ECC83S. I switched that out for another EH 12AX7 and it made alot of difference. To check it all you have to do is push down on the aluminum cover and turn it to the right until it comes off. They are kinda a pain in the *** to get off but don't worry, your not gonna break anything. Check that and if it's a JJ ECC83S I would replace it with an EH 12AX7. They are only about $11.00 and there are several websites that sell all kinds of tubes so let us know if you need a link. I wouldn't worry about the effects loop tubes, they don't seem to effect the sound as much.
Now, on to the modules. Take that Clean module and get rid of it, it sucks ***. I had the Clean and it is terrible. You cannot get a useable volume out of it to compete with the high gain modules when switching channels without it sounding like total ****. Buy the Blackface, it is 100% better. You will love the clean tones it has. As for the high gain modules I think the most underrated module is the SL+. I had the XTC, and Ultra Lead and sold both of them. I A/B'd my SL+ with a 1086 and I think it sounds better than the 1086. I loaded my SL+ with Shuguang Silver Dragon preamp tubes and it absolutely screams. To me the artist modules are not worth the extra money especially when you can buy the original modules cheap on eBAY or here on the forum. I actually like the Recto module. You have the black stripe version so it has the .022 cap. I would swap that out for the .001 cap, it will tighten up your low end. This is a great module for the newer metal downtuned type tones. I use the EH 12AX7's in this module. You have to have some solder skills to switch out the capacitor but it is relatively easy to do. If you cannot handle this I'd be glad to do it for you. I bought a bunch of spare orange drop capacitors and have them handy. I could fix it up for you and turn around in 1 day. Just let me know.
