Replying to my own post, 0.78mm 2pin 2.5mm balanced cheapo cable arrived today and as with my SE846's the K10U sound better balanced vs SE.
The cable is amazing for £15 but I had to use a hairdryer to warm up the soft memory sleeve to bend to a tighter angle as per the included Noble SE cable. Doesn't have an adjuster sleeve to tighten up to chin but can easily fit one over the ends if I need it.
This cable is also good for the K10U as it has the small rectangular pieces around the pins so fits into same recess as the original cable. Many of the 2pin's have a round connector.
I also already have the Fiio 2.5mm to 3.5mm adaptor so can leave the balanced on if I need to go SE.
With both the SE846 & K10U the music sounds more alive/3D/holographic/pristine/distinct via balanced out of the BTR5. Just more organic/musical. Those words come to mind anyway for me.
Said it before, the BTR5 is bloody amazing over balanced either as a wired DAC or via LDAC BT.
Also the BTR5/K10U combo does sound more high-end than the BTR5/SE846 (as it should really).
The sound signature between the K10U & SE846 are different and I will be keeping both. The SE846 is still best for fit and looks better in ear when out & about and are a warmer sound compared to the brighter K10U.
Never thought I'd like anything more than my SE846's but these K10U might just be my new favourite for SQ.