I've heard this before and this is precisely what scares me away from trying (and spending too much money, IMO) the K712. I already find the K612 has plenty of bass. And any warmer (coloring the sound) would completely turn me off. Perhaps my amp and the my K612 are a match made in heaven.
The reason I actually upgraded to the K712 was more of comfort thing, the K612 just wasn't quite deep enough in the earcups and I wanted more refinement to my sound overall. The K712 delivered that. Listening to the K712 more after getting it made me realize I prefer a warm sound overall.