WA6 in a heartbeat! Not only does it have great synergy with HD650's, it is also made in America, meaning that it is SIGNIFICANTLY cheaper to send it back in, should it ever need service
the upgrades are certainly NOT worth it, except for the power tube upgrade - you should definitely get that one
I don't see any power tube upgrades on their site,other than this "Drive/Power tube replacement:
1 matched pair 6DE7 $17 (2 pcs)
NOS tube. Buy and ship independently."
That's the same as the stock tube?
In regards to Little Dot,I tried emailing them,and it came back as not an email address,and,it takes forever to load a page. Didn't give me too much confidence with that company.