EL34 SE as stable with complex music as EL84 PP ?

I 've done a few tests on this very topic and IMO the 34 is not as good in all the facets you mention.

With a speaker that inefficient you will need a single-ended amplifier of much greater power- 50-100 watts, that is if you don't want to drive the amp too hard. Single-ended amps do their best if not driven past about 20-25% of full power.

OTOH a push-pull EL34 amp will likely work just fine. Generally speaking, you get a greater percentage of usable power out of push-pull amps although they tend to have less low level detail than a single ended amp. However push-pull almost always have more bandwidth (SE amps are limited by their output transformers), usually in the bass since most speakers that are efficient enough to work with SE amplifiers tend to not cover the bottom octave.

You can get around the low level detail issue by simply making sure that the P-P amp you get is not too powerful (the reason being that most P-P amps have a certain amount of minimum distortion which happens around 2-5% or so of full power; at power levels lower than that the distortion is actually higher). So if you are thinking of a single pair of EL34s in push pull you should be fine.

My Coincident Dynamo 34SE defies gravity 😀! Best, Rob

You could give Roger Modjeski (Music Reference) a call. He makes both single-ended and push-pull tube amps, with EL34's and other tubes.

The Music Reference amps are superb. I've owned both the RM-10 (EL84) and RM-10. So, second Bdp24, good choice. Most of the speakers they drove were 87-89db, 4ohm. Best, Rob

Meet to say Rm-9 (EL84). Rob

Yes, the Music Reference amps are a good example of how to use the EL34.