I did a quick comparison with my modded Q701s using some songs with a lot of upper-mids energy and not very prominent bass. The K712s are definitely brighter, and the bass port mod on the Q701s gives them a bit more body. Then I did the bass port mod on the K712s. It doesn't mess with the mids, so on brighter stuff I'm still EQing the 2 & 2.5 kHz bands using the Graphic Equalizer component in foobar2000 by about -2 and -2.5, with slight reductions in the two surrounding bands. It's easy enough to reset or import those settings.
I was really surprised at the difference, and that the Qs could seem warmer. And that was using the stock pads on their respective cans, but the same DIY'd Mogami cable on both. The Qs' sound stage did seem a tad larger, and I'm still wondering about that "hole" in the center. Another comparison for later today. The warmth/mellowness factor in the Qs could be due to a few hundred hours on them. I'm not sure how many hours were on the K712s when I got them (pretty sure I'm the third owner), but I don't think it's a lot. I've got some tubes to burn in, so that'll put some hours on them. Curious to see if/how they change.
One note on doing the bass port mod: since I wanted to slide some foam over the ports, I had to remove the screws and pull the plastic housings off. That last task proved a lot more difficult than with the Q701s. So I'm living with that mod for a while before I decide whether or not to keep it, and if I revert, I doubt I'll be redoing it.
So with the mods (felt rings and bass port) and the slight EQ, I enjoyed a nice session yesterday. I played some heavier, darker recordings, too, to test the effect of the bass port mod, and even with the slight EQ, they sounded good. In typical AKG fashion, however, they exposed the indie nature of the production. They play best with really well-produced stuff. Just part of the deal.