You might try out the PT48 which is what I use on my PT6ps. I just recently returned to it again for the 3rd time. It is more round on the inside than the PT50 though it is pretty wide which is something I don't like. The PT6 & 6p are truly fine tubas. I like mine!
If you like Schilke, the Helleberg (not Helleberg II) and the 66 are reasonably comfortable and the diameter is close to that of the 24AW's (I play a 24W on my 981)
