Good day.
Yes, you would want 64bit processing on. Then:
In Settings->Audio.
Mono - Off.
Dither - Off.
Phase Inversion - Off.
Subsonic Filter - Off.
Ultrasonic Filter - Off.
Reverse stereo - Off.
Oversampling - Off.
By Off i mean not checked right.
Normally you would want 'Follow source frequency' to be checked.
Now something to experiment....i do think for most if not every DAC chip out there that the manufacturer says is delta-sigma modulation type one (the two in the Fiio are such), you would want try 'follow source frequency' off, then 'DSD, DSD over PCM (DOP)' checked (to be on). Click on it to show more options. Then check only the first 'PCM to DSD'. The other two native dsd and volume control unchecked. Try that if the Fiio CPU can do the conversion. If you hear cracking noises or distortion in sound, then it probably can't and so turn the whole DSD options off and check follow source frequency again.
If you want try best quality, go further in in the PCM To DSD and check DSD128 format. You could try multithreaded processing if you hear distortion in sound.
There are few situations:
1. You could turn off 64bit processing off and then try DSD To PCM and see how it is. That is if you hear distortion in sound with 64bit on. 32bit+DSD64 to my opinion is not worth it and you will get same quality (meybe even lower quality), with dsd options off and follow source frequency on.
2. 64bit processing + DSD64 is little better than follow source frequency.
3. 32bit+DSD128 you will hear improvement but not a big one. I think this is better than 64bit+dsd64 only if you do not use equalizer. If you use equalizer, then 64bit+DSD64 is better.
4. And best is 64bit processing + DSD128. Here if you do not hear difference, then...well you just don't. But there is improvement in resolution, details, bass and treble responce in general.
You also have all these 4 situations + multithreaded procession on or off and there is also in Playback where the 64bit option on or off, below it there is resampling quality audiophile or quality. This is minimal impact, but there is difference. Audiophile uses more cpu than the other one. Can use it to combine things. You want audiophile checked, but also may try just quality in combo with the dsd to pcm conversion if the CPU can't do it straight up.
I do think this is the best player. Even without the DSD option, it is better with the 64bit procession on than other players. With the DSD is on another level.
These are my settings. Happy listening to your music.