I'll be the "third wheel" here - I own the TH-900 but not the HD 800 or the Z-1R. For electronic music (I mostly listen to vocal trance, progressive house, ambient, future bass, retrowave, electronica, etc - not like "super duper slammy bass" or "eyeball message" kind of things, but that isn't to say its absent my listening experience entirely) I think the TH-900 do a really good job. Specifically they have excellent bass texture, impact, and extension but it is never over-bearing - if the track/content isn't extremely bassy, they don't push an "extremely bassy" version on you, they just let it exist as-is (this is kind of a contrast to other headphones I'd hold in high regard for their bass prowess, like DX1000 or W1000X, which both impart a consistent "thickness" to the listening experience), the mids are very good (clean, clear, well positioned and integrated to everything else, etc) and the top end is energetic enough for all those "electronic bits" to really pop, without being overbearing/harsh/aggressive. Overall they could fit as a good "all rounder" too - they're the kind of listening experience I'd rank 9/10 in any category, they don't achieve absolute perfection anywhere, but they don't really have any chinks in their armor either. Honestly they're an easy grab from the headphone shelf on a regular basis, because I know they will consistently perform no matter what I happen to queue up and listen to, and the comfort is top notch.
To throw another wrench in the cogs: I don't consider the TH-900 the "final word" in headphones, especially for "lighter" electronica. For that, I'd look to the ATH-W5000. They give up some bass extension and a lot of slam to the TH-900, but the mids and treble are significantly more forward, which makes things like horns, strings, higher-range synths, vocals, etc absolutely seductive. They're also faster - this isn't to say the TH-900 are "slow" but I wouldn't regard them as particularly "fast" either. W5000 on the other hand are quite speedy. Now, if you're after something that can drive a hard bassline aggressively, or get into the "eyeball message" kind of genres, the TH-900 will probably suit better because they can reach all the way down there to the depths of sub bass and hammer away at your ears. There's certainly some "compromise" on the W5000 - you get 10/10 in some areas but they "drop off" to 8/10 in others, if that makes sense. When I know I'm going to want to listen to "lighter" music (e.g. vocal-heavy pieces or lighter ambient/techno/glitch/etc) the W5000 are an easy grab, but if I decide mid-way through the listening session to transition to something that really wants to "slam" I either have to put up with the lack of serious response below ~40-50 Hz, change what I'm listening to, or go get a different pair of cans.
As far as drive on the TH-900 (well and the W5000 for that matter) - these are easily driven headphones. They're low impedance and high sensitivity. I've got the matching amp for the W5ks from AT (the HA5000) which provides something murderous like 2W/ch into 16 ohms, but the gain structure isn't awful - I use it with both the TH-900 and W5000. Do they need this much power? Absolutely not! But I think the "point" of this being the companion amplifier is dynamics - its absolutely effortless all the way up to very robust listening levels, and no matter what the music/movie calls for in terms of dynamic range it can just deliver it. The listening experience is similar to my electostats (which are, per their owners manual, apparently able to do 120-130 dB SPL (I have no desire to test this; it would probably hurt)). That said, they can absolutely plug into a PC soundcard or a CD player's output or whatever and still sound great, you just lose that "effortless dynamics" thing - think about highly efficient speakers and big power amps, its not needed, but there is some method to that madness.
Sorry I don't have any insight on the HD 800 or Z-1R (but from reading this thread the Z-1R sound like they might be a serious contender to the TH-900 - looks like you've at least chosen your options well), but I'm happy to talk TH-900 (or W5000) with you all day, haha.