Josh Levinson once bubbled...
The only thing I would all this is that I don't like the reasoning that your backup regs (either 1st or 2nd stage) should be of lower performance than your primaries, because they're only backups. When you have a problem underwater and you need to switch to your backups (whether it be regs, or whatever), they better be in good working condition or you'll be in for a pretty unpleasant surprise. If your regs aren't of equal performance, if anything, the backup should be better performing than your primary.
As for the Apeks... I use TX100s as my primary and backup. They're very good regs, and I haven't had any problems with them, but I've breathed other regs which seemed just as good under similar conditions (but I haven't really pushed my regs to the limits).
About the routing, whether you do cave diving or not, I think proper routing is important for any kind of technical diving. I'm happy with the routing config of the TX100s, and for stage regs, having a swivel is kinda nice (although I'm sure I'll be yelled at by many people for saying that).
Good luck making your decision.
Josh