DanG -
I was using the Valve Art Nickel Plate 300Bs from Angela.com, and they are quite good. Kevin Deal opined that they don't quite have the magic of the WE's, but agreedthey're quite good. At a hundred and change per PAIR that was fine for me. it wasn't the individual tube that was lacking, the 300B is just too far gone in the romantic direction for my taste, especially with the Senn 600s. I also tried the Valve Arts in the AES SE-1, which will accept 300B's or 2A3's, and preferred the 2A3's. They offer more extended bass and treble and somehow sound "faster" than the 300B's (in that amp, in my system.) The preference lead me to sell my Meadowlark Kestrels for Soliloquy SM 2A3's, and swap the 300sei for a pair of Cary 2A3 monoblocks, which are now for sale. If you've swooned over the 300sei, you should hear the mono 2A3's!
The ZOTL will allow me to try both the headphone output and the speaker output, which should be interesting. My main ams are monoblocks which sit behind their respective speakers, with 3 feet of unterminated solid core silver speaker cable between them and the speakers. They're 7 feet apart, which doesn't lend itself to headphone use, and I wouldn't want to break off bits of the spkr cable disconnecting and reconnecting them all the time.
I will hook up the AES SE-1 as a dedicated headphone amp for the AKGs off the 2nd pre output on my Audio Note M-2. Then I'll fire up either the AES or the Bottlehead amps depending on which I'm going to listen to. I'll also use the tape out to feed the Melos SHA so that I can run the ZOTL, AES and SHA all at the same time (disconnecting the Bottleheads for those sessions.) This is going to be fun! I'll have to try the Cary 2A3's with the AKGs before I let them go, and I'll try the Bottleheads as well. I'm incorrigible!!!
Evilcthul - I bought the 300sei used on Audiogon without tubes. The seller wanted $2000 with WE's. I already had a couple dozen 6SN7s and some 300Bs, so I bought it empty.