Please give me some suggestion on tube amp

Hi all,
I'm in process of upgrade my 2-channel system and need your suggestion/help. My current system:
Theta David II transport
Stax x1t DAC
Clearaudio Champion Level II
Clearaudio Tangent Linear arm
zyx airy 2 Cartridge
Tom Evans Groove phono
Emotive Audio Sira-LE
Mastersound Reference 845
SAP J2001 MkII (Italian Hybrid Horn)
Nordost, Siltech & Virtual Dynamic top of the line
Hydra 8 (original)
PS Audio high current AC filter
Symposium Rollerblocks Tweak
SAP speaker stand Special for the J2001 Tweak

I'm happy with the system right now. However, lately I want to try bi-amp with the speakers to bring out the max performing. I just ordered a crossover from Marchand, model XM-126S-2AA, 2-way crossover, all vacuum tube w/separate power supply; low pass filter @ 800 Hz w/ 12dB per octave slope; high pass filter @ 800 Hz w/12 dB per octave slope; with attenuators (since my preamp only have 1 output).
I will have the Mastersound (40w/2x845 tube per side) for the high and mid. So here is the question. What tube amp should I get for the woofer. My budget range around 3-5k. Any suggestion and recommendation will be greatly appreciate. Thanks!
Link to my current system:
http://forum.audiogon.com/cgi-bin/fr.pl?vopin&1114297169&view