nice upgrade, that certainly helps the speaker cable search.
as i said, the mac ultra silver+ cables sound great on mine. many cables, as you know, sound too muffled on old marantz gear - cardas, for example. so i would tend to get a cable with some silver in it - another cable i've had great success with (on the marantz and pretty much everything else i've tried it on) is the van den hul bay c5 hybrid, which has a silver-plated copper conductor and just sounds "right" everywhere to me.
interestingly, i've had very pleasing results using matched digital cables as interconnects (for analog, that is) on vintage gear. i don't know if something about their impedance works on old gear or what, but i still use some audioquest yiq-1s to connect the audio signal from a cable box to the marantz and i like it a lot.
speaker cable is more flexible with the marantz, the belkin i mentioned earlier would still fit your needs, i think, and if it can still be found on sale, the price is ridiculously low. i can't speak to too many "bright" speaker cables, as in general i'm trying to minimize brightness, but if you REALLY want to get bright, some nordost blue heavens or red dawns would do that (blues, particularly). audience conductor (konductor? can't remember the spelling) would probably sound great, too, if you could audition it.
good luck!
