Designer boxers briefs are a nice gift. Underwear as a gift should be chosen like any other piece of clothing -- get him something you think he will look good in. Only instead of "this sweater will look nice on you" you're saying "these will look hot and make me want to yank them off you." It's the same thinking that goes into him picking out some lingerie for you.
That said, remember comfort. Boxers aren't a piece of lingerie that he'll only wear during sexytime. Ostensibly he's going to be wearing these boxers when he's alone with you and also when he's at work in a long meeting. So opt for the most comfortable fabric. Also keep in mind his style. If they're too tight, and he normally wears loose-fitting underwear, he's probably not going to wear them all that much. Guys appreciate when you consider their comfort as well as their style.
"Ostensibly" ? Lol! Nice, Chic Geek, nice.
"Guys appreciate when you consider their comfort as well as their style." PSST...., so do the ladies, Nick.
(Boxers aren't a piece of lingerie that he'll only wear during sexytime.)