VSA manual does suggest that they will sound better bi-wired or bi-amped.
Also, I am not clear as to how to vertically bi-amp. My speaker cables are not identical, I'm using MIT on the bottom end and Synergistic on the top.
I called VSA when I bought my VR4s - Albert answered the phone personally on the second ring! I asked him about biamping or using a single high powered amp (I was considering having my Eagle 4's converted to Eagle 11 mono blocks. He said they're best when biamped. I've since tried them with several different amps and none best Eagle 4s in vertical biamp config.
Vertical biamping is easy - but you need identical amps. One stereo amp goes to one speaker, the second to the other. Connect one channel of each amp to the mid/hi, one channel to the bass. You can use different cables for mid/high if you like. There is a biamping thread in the archives where Steve McCormack describes at length why vertical biamping preferred when you're passively biamping. It's worth a read Here.. he also discusses using different cables . . .