2 systems one set of speakers?????

I would think for the cost of this elaborate set up that you could easily replace it with something that sounds better then either.

I'm not sure about running 2 sets of cable to the same speakers, perhaps someone else will comment on that. I know of one way you can use both sets through the same speakers, if your amp can take both a balanced and an unbalanced signal. Route your receiver into the single-ended inpur on the amp, and use balanced connections from your preamp. This will only work if your amp has both kinds of inputs, and your preamp can go balanced out. If it can, just make sure you never have both running hot at once. BTW, just for kicks, have you tried running the CD player you like for rock directly into the preamp? If it's the player you like, and not really the receiver, that would make life much easier, as you can have both players in separate inputs on that preamp.

DO NOT run two sets of speaker wires to one set of speakers...you would essentially be connecting the outputs of the two amplifiers together, which is BAD. The only safe way to do this is to have some type of switching box that isolates the two amps. Such a device isn't very common, unfortunately...I'm not sure where you'd find one. A better solution would be to use two sets of speaker cable terminated with banana plugs, and just swap the connections to the speakers.

You can (and should) use a speaker switch in this situation. Connecting your separate amp and the receiver to the same speakers would connect the outputs of the two amps together, and result in damage to one or both units. Quality speaker switches are readily available for little money. Though they are normally used to switch one amp between two sets of speakers, there is no reason they could not be hooked up in reverse by connecting your amps to the speaker-outs and your speakers to the amp-in on the switch.