Are LX3 drivers improved, does it support nowadays more than 4 tuners?

Tested with Sundtek USB-stick and not working.. So it is still 4 tuners max

Yes. It does work with three or less internals.

Attached screenshots, Sundtek with three internal and with 4 internal and always it shows onlly A,B,C and D.
Before this used 2x Sundtek in Vu+ Duo & Solo2 for "years". It must be driver issue.