I suggest you make them "active" with a pair of 200 underneath the voxes; the difference is huge between the vox and the lab version.

I've owned a pair of voxes a few years back and replaced them with a pair of labs; never regretted this and you can even upgrade the labs [there is a thread of this by an expert from germany, who's done this for and by himself in his labs]

The sound quality from your pentas is being constrained by the relatively mediocre amplifier in the BC9500.

Either get a pair of Lab 200's to put under your voxes or use the powerlink output with a special lead to a more powerful stand alone amplifier. There are many on the market but I have achieved good results with a QUAD405

You can do the mod yourselve, it's really not difficult. The mod is for active and passive Pentas.

You definitely don't want to drive them with tube amps. Massively efficient and sensitive, simple speakers are suited to tube amps which have a very low power output, and the Pentas are the complete opposite! You need a pretty beefy amp to get the pentas sounding good. The one in your 9500 won't cut it, and something like a BeoMaster 6500/7000 or a 6000/8000 would do the job much better. The BeoLab 150/200 are good amps, but apparently have deteriorated over time and as a result need a bit of work in order to get them sounding as good as they used to (not that I'm speaking from experience with these, I've only ever seen/heard one pair and they were not in good condition).