this is true and i was about to add. the HPA 5000 and HE-6 combo is very good. and the HE-6 is the better headphone, tonally, and transparently. despite only having 5W, the HPA 5000 has no trouble with HE-6, it doesn't have the headroom a speaker amp will, but its a good pairing. on other amps such as the WA5, the HE-6 also outperforms the HE-560.
alot of stratus owners like the 5u4g, i myself still think its overrated and overpriced, despite actually being an okay tube. the 5u4g didnt sound as good on wa6-se as it does on the other woos or other amps either.
they look like the right tubes, the plates look identicaal to the ones i had from jack, actually these r nicer, the ones jack had at the time when i bought were Westinghouse rebranded sylvanias and they appeared ro be slightly newer tubes.you shouldd be good
the philips 5r4gys is compatible with the WA6-SE, i didn't like it though, was mediocre sounding on the WA6-SE, i found it to be slightly better on other amps. its an okayish tube, thats about it. the CV 593 is much better
yep they're good tubes, but needs rectifier like 596 to balance that bass out, its a nice synergistic combo, but otherwise, yeah very bassy slightly muddled. i like the 6GL7 but the description on the woo website that says you will hear every note with breathing air around it, definitely not true..