Yeah, the GSX Mini drives it well, as does my AK Kann Alpha. There is something about the Pass combo which enhances the R10P's clarity, however.
In terms of comparison with the Susvara, the presentations are quite different, I would say.
- The Susvara has clearly more air around instruments while the R10P has substantially better slam, punch, and more bass energy. The R10P has a darker presentation, overall.
- I would say the Susvara mids are relatively linear, while the R10P appears to have a bit more energy in the 500-2K range, which gives it a more forward presentation.
- The Susvara treble presentation is more polite. The R10P has a peak somewhere around 6-7K, to my ears, which didn't bother me, but one of my audiophile friends felt it. I personally thought it added a nice edge to drum hits.
- Technically, the Susvara has more micro details and a wider sound stage, but the R10P has a pretty impressive SS presentation given it's a closed-back. This cup design is clearly paying off.
Overall, the reason why the R10P stands out to me is that it's more technically capable than other closed-backs in the market, in my opinion, but I am going by memory here.
The other reason it stands out is that Hifiman has really tried to give it a lot of "excursive power" so that works quite well, if you have a Susvara already, and want something less polite, when you listen to electronica, rock, etc. That has been my use case, at least.