You've basically got it right, AJ. Though since Corey already has the UA-5, he could probably run mics>UA5>DR2d(line in) + SBD>attenuators>DR2d(mic in).
You could get the DR2d + a SD card for about $125. If say the budget is $750, and you could get $200 for selling the Avantones, that leaves $825 to invest in a set of mics. So Corey could get a 4ch recorder to meet his needs for 4ch SBD+mic mixes, and significantly upgrade his mics.
Which definitely makes it an option to consider. I had an R44, sold it and got a 680, sold that and downgraded to a DR2d.
I've done a bunch of 4ch mixes over the years, but really had gotten to the point that I wasn't getting much in the way of SBD patches, and wasn't doing much in the way of 4mic mixes. I really don't regret at all selling the 680, and generally am happy enough with the DR2d, but I do sometimes miss the R44. Corey should just buy the R44 so I stop thinking about picking it up myself.
You're right though that the DR2d and R44 aren't really the same thing, even if both do 4ch. The R44 makes doing 4ch much easier, and it is much, much more robust. Still, if you're willing to deal with 1/8" connections that can be spotty, putting together an XLR>attenuator>1/8" cable (or whatever), and don't mind the 2ch at once metering and limited gain adjustments, you can use the DR2d to make 4ch recordings and have more money available to put towards mics (which is what I did).
Some more caveats on the DR2d: if you use it as above for mic+SBD recording (which is probably you're best bet), you will most likely need some kind of attenutors on the board feed, and you may need attenuators on your UA5>line feed but probably not. You can only meter the levels on 2ch at once on the DR2d, so you need to toggle back and forth between line and mic for your metering. The line level effectively can't be adjusted (can only adjust before recording, and has limited range anyway due to potential overload issues). So running mics>UA5>line-in is the best bet, and then you can adjust levels on the UA5 and just leave the DR2d set. The board-feed into the mic input can be adjusted on the DR2d, though potential overload issues can be a problem, so you might want not just attenuators, but adjustable attenuators -- eg, -10, -25, -40 or whatever. You won't be able to run a 4mic recording with the DR2d with this equipment set, since you'd only have phantom power for 2ch from the UA5. If you want to start doing 4mic recordings, you'd need to pick up an 2nd mic preamp.