MC uses SSRC
Foobar uses SoX
SSRC is
fine, as long as they are using it in the high precision mode, but it's certainly showing its age now.
SoX is measurably better, and has more flexible options for both performance, quality, and user preference. (such as minimum phase options)
And commercial products (e.g. iZotope) and better still.
I wouldn't mind the option of SoX resampling rather than SSRC, but I doubt it's something that the MC team want to focus on.
I do wonder about DSD Encoding though, as I have heard that SSRC does not perform very well on especially large upsampling factors.