R-011958 is probably a late 1990s, so actually you have the newest revision in 'G'. The REV F were around pre4000 and the REV C and D were pre500 (i.e. R-0972 = the 972nd Recto made) Your amp was the 11,958 Recto made.
The REV G (or any recto for that matter) are a gain monster, however, the REV G are not muddy, they do have fizz sizzle. The best way to cut out the fizz is to run the treble at about 9 o'clock to 11 o' clock range, cut back the presence and run the gain about 1 o'clock. (Rectos EQing are weird)
IMHO, Sovtek 5881WXT are the junkiest tubes on the market and less quality. From the tones you described, I think EL34 are just what the doctor has ordered for you.
Preamp tubes are the gain stages and a significant part of the tones as well. 12AX7 are the most popular and the hottest. What I do with the gain monster, Peavey XXX, is change out the 2nd preamp valve to a 12AU7, which cuts back the gain. Experimenting tubes is an entirely different world, you might want to read
THIS ARTICLE to help you understand valves a little better. Also check with Eurotubes.com. Bob, the owner, is a great guy and can help you find the best tubes for your amp.
(he even sells different types of packs of tube combinations)
I agree with Brian, your guitar isn't the problem. The Dimarzio super distortion are hot. The Ibanez RG320 are awesome guitars, my buddy had one and I loved how it played. They have a really fast action and are precision instruments.
Like Brian said, you could take your guitar into guitarcenter and play a new Dual Recto to see if it sounds flat like yours. However, I'm leaning towards your tubes are probably dead and lifeless and need replaced. What cab are you playing through? That can make a difference to some degree as well.