The Mojo is much more than just an FPGA chip to run the code Rob has done. It also uses discrete Pulse Array DACs (that he invented) and the discrete analogue section is very clean with extremely good measured performance, plus the battery used is a custom battery specifically made over three years just for the Mojo that packs 14 watt hours.
I love FiiO, and wish them well, but the implementation of the whole system is much more than just FPGA vs off the shelf DAC chip hardware. Sonically I have no doubt that FiiO will produce a good product with the Q5, as they have with most of their lineup. I'm simply pointing out that the Mojo's advantage is the pedigree it comes from, which is the exact opposite of where FiiO has come from. The trickle down tech of Chords products puts the Mojo in a different class on a technical level.
To be clear, I'm only sharing my knowledge here of what I know of Rob Watts tech (you can read his many informative posts to learn as well). I'm NOT saying one will sound better over the other, no one can at this point.
At the ears each user will have a different opinion and at the end of the day that's what is important. I think it's a waste of time to compare the Q5 on a technical level because it simply won't compete to the Mojo. Let's wait until the Q5 is released and go by sonic impressions. After all, that's what REALLY matters.