I think you really need to read the note on the Foobar2000 ASIO plugin page...
I cannot measure anything on audio tracks of course.
What was measurable was higher count of ISR and DPC calls compared to WASAPI, and audio driver could take up to 60 microseconds which is 5x more than with WASAPI or default. It simply indicates that audio is taking much more time, but also higher priority to process.
I was definitely not expecting anything audible, only in cases where I could confirm presence of resampling or anything related.
There are few instances where sound which is definitely on the track became more audible - like there is a track where drummer hits the sticks by mistake and bassist hits the strings 3x almost inaudibly during intro...
Strange... do not expect a difference, let alone a big one. Possibly one of them is 'broken' as implemented on the Realtek codec (my bet would be Asio), or the volume differs...or you're imagining things.
I am surprised, it makes sound, not even that it sounds good. I use Realtek only for its digital output, so the processing should be minimal anyway.
Also regarding MPC HC...
There is ASIO audio renderer - MBSE Multichannel Asio Renderer - it claims it renders audio in 48KHz 32bit FLOAT format, which does not make much sense... Output is Optical SPDIF and DAC is capable just 24bit sound.
There was a tool which allowed to display each object in an active sound chain from file, through application, all filters and driver... I dont remember the name...
A presence of an APO or transform filter in one or another setup would explain it.
edit:
Did some listening tests with Foobar ASIO plugin VS Wasapi and Default.
Wasapi Exclusive and ASIO sound the same. WASAPI plugin requires to specify output bitrate. If its not matching the source, there might be transform filter involved...
ASIO sets output bitrate automatically, apparently on the same value as media file. but "pause" does not work.
'Default' sounds slightly less loud, and some detail is missing.
For MPC HC
- WASAPI Exclusive is possible through internal filter in MPC HC. It uses limiter and volume filters. At least it does not lie about 32bit FLOAT output and reports correctly its being reduced to PCM 24bit padded before sent to DAC.
- ASIO Renderer allows better transform filter than windows default, again allows output samplerate and bitrate to be selected automatically and in bit-matched manner.
- There is little to no difference when using 'Default', again slightly less loud...
Both ASIO audio renderers are exclusive by default, in case of Foobar introducing few small advantages.