The SP1000 supports a wide variety of audio formats including WAV, FLAC, WMA, MP3, OGG, APE, AAC, ALAC, AIFF, DFF, DSF, as well as native DSD. The player is equipped with dual AKM AK4497EQ chips, which provide a playback resolution up to 32-bit / 384 kHz and native DSD playback of DSD256 (1-bit / 11.2 MHz). It also plays MQA.
The SP2000 plays MP3, FLAC, WAV, ALAC, Ogg Vorbis, AAC, AIFF, WMA, DFF, DSF, and MQA file formats
When I had ISOs, I simply converted them to DFF/DSF (I forget which, I stopped playing DSD-type files years ago). If AK doesn't offer the features you need, there are so many other brands that it shouldn't be hard for you to find one that does offer what you need. AK prices are their prices, they sell lots of devices at their price points, and the exclusion of an ability to play ISO files doesn't seem to affect their sales.