For the benefit of anyone else who might be interested...Two pieces of potentially unwanted advice:
1. vacuumtubes.net is selling NOS 5998s for $85 each. Frankly, I would just buy from them. The price is reasonable, and if there is a problem you can return the tubes.
2. Have you ever heard a BottleHead Crack (with or without the Speedball)? If not, I highly recommend that you skip the WA2 and build (or buy) a Crack. I bought and built one on a whim. Immediately thereafter I sold my balanced Beta-22, my Woo Audio WA22 and my WA6. The WA22 was running $600 worth of tube upgrades, and the WA6 had dozens of upgrade tubes and adapters. The Crack is absolutely astonishingly good with Senn. HD600s/HD650s/HD800s and with high-impedance Beyers. The combo of the Crack + Speedball with my HD800s literally takes my breath away. Check my profile...I have heard a LOT of headphones and amps. The HD800 + Crack combo is the best I have heard yet. Among other things, it is better than my HE-6s + EF-6 combo. I have always loved the HD800s, but they were transformed by the Crack. The clarity, detail and bass impact is stupefying. I never knew the HD800s (or HD600s) could produce bass like this, nor could I have imagined that an OTL tube amp would provide better detail and clarity than a top-of-the-line solid state amp. Now, I have no doubt that the WA2, which is also an OTL design, is a fine amp, with the usual bomb-proof Woo build quality. But I would rather have my Crack any day of the week. And if you are determined to spend more money, I think you would be better served by building a Crack, adding the Speedball, and then upgrading the film caps and volume pot (to be clear, none of this is necessary -- the stock Crack sound wonderful. The Speedball was a noticeable improvement; whether adding boutique caps and an expensive volume pot has made a meaningful difference is a matter of debate). But there is no question that you can build a Crack with super-premium parts and still come out cheaper than a WA2, while also having a custom amp you can be proud of. BTW, in case you are wondering, the Crack is easy to build, with excellent instructions. I built mine in two evenings and got everything right the first time, even though it was the first amp I've ever built.
Lastly, you might also want to consider buying a Little Dot Mk VI+. It is a fully-balanced OTL design and comes very close to the performance of the Crack (very, very close), yet is also capable of driving my HE-6s with ease (frankly, it has more power on high gain than my EF-6 does). As an added benefit (and this was wholly unexpected), it is aesthetically more attractive than the Woo gear, including the WA22 when running a Sophia Princess rectifier. I didn't realize this until I got it, but the analog meters on the front are illuminated and look gorgeous in the dark, as does my glowing quad of 5998s.
In short, buy a Crack + Speedball, and order a single 5998 from vacuumtubes.net. You won't regret it...