So this is just a lot of guess work since I own neither at this point:
I think the output current of the X5 is 460mW into 16ohms (according to Fiio). I'm assuming Fiio capped it at 460mW, so it should still be that at 9ohms, which is A LOT for an IEM. It's almost half a watt. Your 846 will be thundering.
Thiis is not current, it's power. Divide the 16ohms from the 460mW and sqrt it.
The voltage gain on both the DX90 and X5 is 2.8Vrms (according to spec). Assuming this is true, and ignoring that Chinese dude's measurements the DX90 has the potential to match the X5 in terms of current, but I'm not sure if Ibasso capped it lower than Fiio. I think they might have. If you're looking for max current I think X5. If you're looking at other sound quality factors, perhaps DX90?
This is not gain, voltage output at a gain.
Obvioiusly this is just a guess and nothing more than preliminary musing based on nothing. What's ironic is that the DX90 actually has the bigger voltage swing, which is 10v p-p, while the X5 does >8V p-p. Not sure why Ibasso capped it so low? perhaps to achieve those nice THD numbers?
To be perfectly honest I'm pretty much baffled by Ibasso's numbers. Why?
Because according to them the DX90 does +/- 5V,
which is 10 Vp-p
which means it should be doing 3.54Vrms at 32ohms and giving us 391mW at 32ohms (more than the X5)
Instead they say on High gain it's doing 2.8Vrms, but this Chinese dude is measuring it at 2.1Vrms. I'm assuming they capped the max current for headroom? Fiio's numbers actually align perfectly with their stated peak to peak values and what the dude measured, in fact it exceeds the numbers by a little bit.
Yes, it should be around 3.5Vrms around most load since output impedance is less than .1ohms. I get 110mA for current. W is power, not current, but yeah 391mW is what you should get at that load of 32 ohms assuming it's can provide 10Vpp at max volume at max gain. The low output impedance maximizes the power to the load so most load should get close to maximum.