I was under the same dilemma, waiting for SACD ISO support. decided to go ahead purchase the M6 and load Neutron which plays SACD ISO, the experience was marginal Neutro is very good player but the overall sound quality is behind the shanling app, even playing my SACD ISOs. As I mentioned before, I really exceptik of the whole DSD suposedly superior sound quality. When I used to play my SACDs with Oppo CD player the experience was spectacular, the player died after some years, and I moved to all digital + external DAC (Yggdrassil).
Buying the Ygadrassil was big decision, as it does not support DSD. I have stayed with PCM files only since then, and have not have the opportunity to really try SACD and compare then to FLAC/PCM.
The only test I have been able to perform is my SACD converted to DSD64 Vs the same song in FLAC. No difference to my ears, both sound amazing tough.