Since no one else has chimmed in.I have had good luck with Electro Harmonix in most applications and they are a good value. I have no experience with cryo'ed tubes.
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I will say that in my Ayon CD5s the 1980 NOS 6H30 DR's made wonderful difference but as you say expensive. Parts Connextion PCX sell 1986 NOS 6H30 DRs for about 100 bucks each (1/3 the cost of 1980s) and from what I hear PCX feels they sound as good as the 1980's.
Hope this helps and that you are enjoying your unit!