X14 Digital output.

My knowledge of Hi-Res audio is pretty limited, and the term does cover quite a lot of ground. I have heard that 24/192 via toslink can require a very high quality optical cable as 24/192 is the theoretical maximum for toslink. Also there are reports that MQA may not play nicely with some digital volume controls, so perhaps try setting the digital out volume to fixed. The Acoustic Energy Aego 3 specifications do not mention MQA so I doubt that it will decode the MQA components of the file, but in theory it should replay the CD like portion of the file.
I would suggest a bit of trial and error to see what type of Hi-Res files will play and which won't. Perhaps make a Hi-Res test album from some of these free samples below.

There's a good range of Hi-Res test files in FLAC and DSD here: www.2l.no/hires/ (Note: clicking each item plays the selected track, then click the three dots on the right for the download option)
24BIT/96kHz - 24BIT/192kHz - 24BIT/352.8kHz (FLAC)
MQA stereo original resolution - MQA-CD 16BIT/44kHz (FLAC)
DSD 64 2.8224Mbit/s - DSD 128 5.6448Mbit/s - DSD 256 11.2896Mbit/s (DSF)

Hi-Res test files in WAV here: www.soundkeeperrecordings.com/format.htm
16/44 - 24/96 - 24/192 (WAV)