The LFT-8b is a pretty-stable 8 ohm load. The LFT m/t panel itself is an almost purely resistive 11 ohms, so good with tubes. If you bi-amp---with any old solid state amp for the woofers (180Hz down) and your excellent Quicksilver amp for the panels, you may find happiness.
If you like the LFT-8b panel a lot (I do), look into the OB/Dipole Sub offered by GR Research in collaboration with Rythmik Audio. Unlike any other sub on the market, the OB/Dipole plays up to 300Hz, and can be used in place of the LFT-8's woofer. Imagine dipole operation from below 20Hz to over 20kHz!
Details on both the GR Research and Rythmik Audio websites, discussions about the sub on the GR Research section of the AudioCircle Forum.