Hey man - sorry, was about to get to your PM - replying here.
The Cayin IHA6 is good for its price, but I wouldn't buy it if you could get a Roksan K3.
Why I would get a K3 over an IHA6:
- The IHA6 treble can sound etched and dry
- K3 has this "spicy" treble which works really well with the Susvara, IMO. It's energetic and now that I think of it, I may even like it with the TC given I tend to need more treble energy over time, with any headphone, lol.
- K3 has a bigger soundstage, in width and depth
- K3 has more slam and punch, as they say. It's quite a dynamic signature.
- K3 has an overall more refined sound
- Might be less important, but it's a brilliantly built amplifier
Why I would get an IHA6 over a K3:
- Price
- Form factor (but it's heavy for its size)
Also, the distinction to be made depends less on absolute output power of your amps. Good speaker amps, if you have seen their innards, are built differently from the ground up, from the size and quality of their toroidal transformers to other aspects of their circuitry, to be better at current delivery.
So let's say you are putting in X watts from a Cayin IHA6, and the same X watts from a K3, hard-to-drive planars like the Susvara will sound bigger and more impactful on the latter.
I don't actually remember the sound signature of the Flux. But I do remember some of my friends recently trying it and thinking that although it powers the Susvara and it sounds quite nice, they didn't like the SQ overall - compared to their preferred amps for the Sus.
But you could always upgrade later, if you know what I mean.
The Susvara is hard to drive but sounds quite lovely even from a Topping A90 or an IHA6.
Hope this helps.