We've tried double-anal penetration (DAP) several times, for the most part without real success. Traditional DP (vaginal-anal) and DVP (double-vaginal) are pretty routine for us in encounters (MFM and FM+ gang-bangs). These positions take some skill.
The only time KK successfully enjoyed DAP was during a gang-bang - she was in an absolute sexual frenzy, almost a fugue state, and the two guys that completed the act had relatively long, skinny cocks.
For us the usual outcome with DAP is both guys cum way too fast from all the friction, one guy may get in deep, but the other barely gets his cock-head in before both guys blow their loads.