Only one bad on DX90 is, that here is Coax Out and not Coax In.
DX90 have very good DAC, so I have not any idea for what I use Coax Out.
By way of contrast Caox In is extremly usefull - CD/DVD/HDD players, TV, game sound cards (too with Dolby Headphones), high quality usb to spdif adapters and more, more, more other.
I want DX90 rev.2 with Coax In
Why do you need a Coax in? Are you going to feed DX50 or X3 to DX90?