I have not heard the FSP but currently have the VK-30SE in my house on loan to me until my VK-50SE gets back from a friends. The BAT preamp is the best preamp I have heard. Whether you buy the 30SE or 50SE, I have not heard anything that can touch them. I have owned the ARC Ref 2, which is a tremendous preamp and only sold it because I was going integrated when at the last moment I heard the BAT and was blown away. The 30SE has an advantage over the 50SE if you listen to LPs. You can add a phono stage to the 30SE for only $500 which is not available in the 50SE. The 30SE is also almost identical to the 50SE sonically. The BAT has long life 6H30 "super tubes" and comes with a 5 year warranty on the equipment and 1 year on the tubes.
I wish I could be more help with regards to the FSP.
I wish I could be more help with regards to the FSP.