What virtualization solution should I try next, after hitting problems w/ VMWare Player in dual-network setup?

VirtualBox has improved leaps and bounds in the past ~18 months in the area of network configuration (I too recently had a similar problem when switching to wireless). While it may not be as "low level" as your looking for, I think it's worth your time to at least try it out.

I answered your other question... It's not that tough to do what you want to do with vmnetcfg...