Mcpherson
I own Focal JM Lab 936 non Berylium tweeter speakers and it took a combination of things to get the tone I wanted. You have to ignore all the negative crap you will read about trying to adjust the tone of your system. In my mind it is my system and I want it to sound the way I like, not the way some one else delares is correct.
The tubes you want to warm up that tweeter is most likely going to be a good old stock 12AX7 Mullards from the 50s or 60s that you put into the pre amp. The Blackburn long plate in particular. I think Brent Jesse at Audiotubes.com may have them. These are warm tubes, but be aware that almost any British tube is going to lean towards the warm side. If you can roll input tubes into the HK again look to Mullard for the best results.
The other things you want to do- although this will cost quite a bit of money- is to get Cardas "Golden" whatever interconnects, I have the Golden Refs. These copper interconnects really make the Focals sound great. I also suggest good copper speaker cables. Again ideally Cardas or Jena Lab but both do cost a lot even used . I would never the less look for them to show up. I lucked into some used Jena Labs and the sound is fabulous.
I happen to have an AE-3 Pre Amp by AES a Cary brand which uses 6SN7s which are delightful tubes for smooth and rich tone, it made a world of difference in my system. Good Luck!
