Dan,I have used the 4 Pi-pro with great success on 45/2A3/300B/EL34/EL84 single ended amps with less than 7 watts output.
I also have used the JBL 2226J which is a 16 ohm driver with the 8 ohm taps on the SET/SEP amps with great sound due to the increased damping to the output tranny's.
Do a search on this forum and see posts I and others have made in this regard. There is much info to be read concerning this topic!
Hope this helps!
Regards, Ron