That's some bad info on the Prologue 2. The adaptive auto bias on the Prologue 2 allows you to use KT88, 6550, KT90, EL34, 6L6GC, 7581A, and KT66 tubes.
Cayin TA 30 vs. PrimaLuna Prologue
Seems like the Cayin and Prologue are quite similiar in Basic architecture ... perhaps mfgr by the same CHinese OEM. However, The PrimaLuna ha smany added and very usefule features. I am told the Cayin has a US modifier .... but I wonder why go throught the expense and hassle of all the mods if you can one can buy the Prima Luna on Audiogon without risk of modifications for the same price?? Anyne experienced with these brands?