28 is fine, especially with two per channel. Good luck with sleeving it in the teflon. After 4ish feet it can be a real pain, YMMV.
The solid core is an issue though. It's fine for interconnects that won't be flexing or moving much, but as a headphone cable and being braided you risk breaks in the line. It will also be quite stiff.
I know about the stiffness. It will be serve as a test only en then they will serve as an interconnect. Stranded is more expensive.
I think I will use one wire per channel without braiding them. Then I have three or maybe four pieces of one meter. and not 6 or 8 pieces of 1,xx meter. Altough I do have 30 meter.. hmmm tough choice. :P