I have the 6, 22, and had the 2. I also have two versions of the 4.
The WA4 (2004) uses the 6C19, 12AU7, and 6DJ8 tubes.
The WA4 (2011) uses the 6C19, 12AU7, and EZ80 (rectifier).
I've never heard the 6se. I would say that the WA4 (2004), to my ear, is closer to the WA22. The WA22 may have an edge because of the rectifier (5U4). But my WA4 has been modded and has Black Gate caps and V-Caps so it has a strong bottom as well. Here are pictures of the WA4 that I purchased. http://www.head-fi.org/t/517160/sold-woo-audio-wa4-upgraded-amp
The WA4 (2011) has a cleaner sound (it uses the EZ81 or EZ82 rectifier) placing it closer to the WA2 but with a slightly warmer presence.
Edited by Clayton SF - 12/15/13 at 3:27pm