I used to have an EVM-12L in a 1x12 combo (Mark III) and didn't like it. I found it very bright and stiff (not bright in a harsh Celestion kind of way, the top end is quite clear... there's just a whole lot of it). For lack of a better description - it was kind of a boring speaker.
From reading various comments over time a lot of people feel the same way. The speaker seems to excel in ported cabs (which is what it was designed for), and an open back isn't the best choice of enclosures for it.
If you're having issues with the amp being too dark, try bringing the treble knob up to somewhere between 1:00 and 3:00. Due to the design of the preamp the treble knob controls the overall tonality of the amp more than it does the actual treble and raising it up opens up the voice of the amp. Use the presence knob to control the actual treble.