Charles, excuse my ignorance, but what are the salient differences between the two tube camps?
I had never got on with tubes full stop, being totally put off them by the stereotypical over warm wooly sound portrayed by BAT eg. But seven years ago got bowled over by the tube Hovland HP200 pre and found this sounded great with the SS Radia amp, servicing my Pro Ac Futures 2, then Zu Def2s and now 4s. Just love the combination of tube liquidity and SS neutrality.
Interestingly the 4s are so transparent and revealing I'm detecting a hint of hardness/coolness which I attribute to the SS Radia, and am really tempted to investigate all tube. Let me say this hardness is only a hint and may well be eradicated by careful choice of cabling (considering all Zu Event) rather than amp change.
So we have SET eg Audion Black Shadow, championed by Phil v OTL eg Atma Sphere championed by UK Zu dealer/Dave Berning ZOTL, much favoured by Roy Gregory in the detailed review of the Def4s in Audio Beat.
How do their respective pros and cons stack up, esp. in respect to listening thru the Def4s, with a very neutral revealing front end (in my case direct rim drive tt with air bearing linear tracking arm Trans Fi Salvation/ Terminator T3Pro)?