The first littlebox production run has sold out, but there will be more available in mid-Oct.
The LB is a preamp only though, no digi out -- though it does have phantom power. So you'd need to run the iriver analog in, not digital in, which can be done. The R09 might be better on analog inputs than the iriver, plus it is 24bit, which are some of it's advantages. Still, I'd bet littlebox (analog) > iriver would sound better than UA5(digital) > iriver based on what I've heard from the LB, and what I've heard from the UA5. Obviously, at this point you get into the realm of opinions. FWIW, I've done and posted a comp of the LB to a Lunatec V3, as has Chuck, and Chuck also ran the Naiant pre analog into an iriver, so it might be worth digging up those comps.