All of Rob's current DACs sound genuinely excellent, even with 16/44.1 (I'm not saying that to be sycophantic or fanboy-ish - Rob's WTA filtering, and other methods, genuinely do make 16/44.1 sound noticeably impressive).
The biggest influence upon how good Mojo sounds, when being fed a bit-perfect digital source signal (by which I mean no software Android software upsampling or EQ interfering with the purity of the digital signal encoded in the digital music file) is how well-recorded the original performance is, and how well-mastered the track was, in the studio.
Higher-res files than 16/44.1 Redbook can potentially improve SQ somewhat, but not to the same degree of significance as the recording and mastering quality, so that should be what you aim your attention for, first & foremost, when buying music to play on Mojo.
In other words, if it's badly-recorded and/or badly-mastered, then creating a higher-resolution file from that source track is not going to make a silk purse out of a sow's ear! Garbage-In, Garbage Out, etc. etc.