I took Meepit's advice and invested in some Andrew Christian underwear, the show-it line.
Here's what I have to say..
They are pretty much what I was looking for. Perfect for holding my STP packer in place.
I got three different styles:
1. Basic show-it boxer
2. Show-it flashback
3. Flexsoft boxer with show-it tech
Id have to say 1 is probably the best, its also the cheapest.
3 is the softest and thinnest.
All are thin and smooth, the material is very comfortable. The "pocket" is perfect to hold your junk in place. The only thing is that the boxer briefs are more like trunks, they are short. I didn't think id like that, but they actually aren't that bad.