I'm possibly one of the few men who would agree with you re: underwear, so perhaps this will give you a glimmer of hope.
Unlike what seems to be the majority of guys, I've always had the "bubble butt" look... but it's more genetic, and not all muscle from having had to do 4,537 squats per week to build up the muscle. Consequently, there's a bit of "give" back there (no "buns so tight he was bouncing off the walls", thanks Pats) but still a (IMNSHO) great looking butt (and considering how often it gets groped in a bar, I figure others don't seem to disagree either ).
SO.... I find that regular briefs have this annoying habit of cutting into said extra flesh and giving me not only VPL, but this weird extra "crease". Tres not glam.
Other "sexy" underwear has a similar problem: if I buy is "supposed" waist size, it's too constrictive. Next size up seems to be way too baggy/uncomfortable.
To be honest, boxer briefs were my salvation. Sufficent support front and back, without the chance of "double butt" syndrome, LOL.
So take heart that there's at least ONE guy out there who suffers underwear problems with you