Yes the 902 and 502's are warm, but they're not overwhelmingly so, and I have no trouble taming them. However, the UL212 is quite a deep sounding cab. It's certainly the warmest of the 2x12's in our store. Have you noticed that some 12's sound like biggish 10's, but others sound more like smallish 15's. Using this analogy, IMO the epi UL212 sounds like a couple of smallish 15's.
If I were you, I'd do what one of our fellow staff members has done (TB member Evan_S_Brown) to his UL902/UL212 rig and add a UL210 to provide the punch while maintaining the warmth as well. This is a killer rig!!
If that's not an option, then I'd look at changing the cab first, and perhaps wait and see how the 902 goes with a punchier cab before changing the head.
I agree with the above. The combination of the voicing of the Epi amps with that particular big, wide sounding cab would not be my idea of a good time if you wanted punch and a more forward tone. However, I actually find the UL210 even wider and bigger sounding, and wouldn't think that would help much.
Interestingly, when I tried my 502 with my very tight, punchy, Bergantino AE410 (it's a mid punch and grind machine), I didn't like the matchup at all. That creamy, fat, warm Epi amp tone still came through. It was like the Epi sucked the punch out of the AE, versus the AE adding tightness and punch to the 502
I've never found an amp that I liked so much in a solo setting, but was so frustrated with in a gigging context, exactly for the reason the OP stated. Again, there are many posts describing these amps as 'dark', which supports the OP's comments.
Per Joker's comment, a pair of UL112's will help a bit versus the UL212, but my recommendation would be to try another head with the cab. There is just something missing in the voicing of the Epi amps to my ear that results in that big, fat, warm beautiful creamy, smooth tone that sounds so good solo but tends to sound dark and non-distinct in some playing contexts.
IMO and painfully IME.
Edit: Of course, there are some that love this fat, warm, creamy, mellow voicing. I don't mean to dog on the Epi amps versus just mention that I hear the Epi amps similar to the OP, and again to say that the wide sounding 212UL makes this issue 'worse'.