They were NOS EL34 XF4's. There is no doubt the BHSE brings out a lot out of the SR-009s. I enjoyed them a lot (naturally a lot more than my Electra even with XF2s). Without the Susvara in scope for comparison, the SR-009/BHSE would be a "practical" top "to own" setup.
However when including the Susvara into the comparison, I have to say I enjoy the Susvara and the MC275 combo more. There other amps that make the Susvara sing but I quote only the MC275 as that was the only (Susvara/MC275) setup I had to compare against the SR-009/SR-007Mk1/BHSE. That was performed over an extended period (let's just say more than quite a few days).
Now for a simple setup, a few weeks ago, I went to the local (e-earphone) store and tried the Susvara off the AK ACRO L1000 and I have to say, single ended, with the L1000 it actually managed to drive the Susvara at pretty decent and acceptable levels with the ACRO L1000 at max volume. I tend to listen a little louder than others and I'm not jesting when I say that I'm actually rather impressed with that setup. The shop did not have a balanced cable therefore I didn't get to try balanced nor off the speaker taps with the HE adapter. I'm particularly curious if the ACRO L1000 15W/ch @ 4ohm speaker taps would be enough to drive the Susvara with even greater authority than than the off the single ended headphone out. If the ACRO L1000 can with its speaker taps, that maybe a rather practical "cheap" DAC/Amp Susvara combo.