From what I could grasp, the base denomination is 12AU7. Because the tubes can be switched, the advertisements on ebay include all the derivate denominations that are compatible. Compatible, yes, but not identical. The 5814A for example is a special version, military grade that requires more power (gets hotter) than stock tube 12AU7. The more current required by the 5814A (175mA instead of 150mA) brings better dynamics. And yet, it also depends on the brand, there are many GEs on ebay but Sylvania and Telefunken seem to be the best ones (see website below). If you say that the 6189W sounds like the stock tube, they may be close in construction quality.
See: http://www.audiotubes.com/12au7.htm (Short cut and paste from the site below)
12AU7 / 12AU7A: The common USA version of this tube. RCA, GE, and Sylvania actually made most of these tubes, regardless of brand on the label.
ECC82: This is the European version of the 12AU7, and is identical to it. The brands in demand are Telefunken, Amperex, and Mullard.
6189 / E82CC: This can be both a military spec tube and a premium industrial tube. Often, the military versions will be marked 12AU7WA in addition to having 6189 etched in the glass.These are excellent step up tubes in the 12AU7 family, when you can find them! Look for super rare triple mica versions from Mazda, Siemens, and Mullard, some with silver plates. Among the best 12AU7 tubes ever made.
5814: This is a military spec tube. These are all low microphonic thanks to their rigid mica supports. Older versions have a third mica spacer near the top. These "triple mica" versions are in great demand today. These vintage tubes have just started to become a hot item, as NOS stocks of the West Europe types become harder to find. These tubes can withstand many on-off cycles and mechanical shock without a problem.
Personally, I have been wondering about the triple mica version of the Sylvania 5814A. But I am not willing to pay $100+ on the pair so the base Sylvania 5814A will have to do (ebay, yeah me too). However, if you guys got any of the triple mica Sylvania 5814A to test with the wa7tp, please, leave a comment about your impressions.
Cheers,
Note: I think finding the best pairing (<5% matching or grade "platinum" by some ebay sellers) will have a profound effect on the sound quality. I read that the major issue with the wa7 could be a mismatched in stereo channel or tubes. Sure, it may not be related with the PSU but I am a perfectionist anyway.