Both units you mention are basic a/d converters, I'd imagine the Edirol would sound fine, as it uses the same a/d converters as the Roland VS range.
Your problem is a lack of mic level input, you can't plug a standard mic into an RCA connector, and the condensor mics require 48v power (otherwise known as phantom power).
I still think a mic like the Oktava or the popular AKG C3000 plus a nice little pre-amp is the way to go, or there is a lovely little package from Joe Meek which is a mic and pre-amp (
http://www.joemeek.net/specials/index.php) its the P3TP: P3 / JM27 TrakPak at £169 it's a steal, plus its red. (?) You'll still need the converter obviously.
You'd need to source the leads to go from the pre-amp to the converter, but anyone with a little electrical knowledge can put them together.
Other options include the ProTools M-box, which has mic amps (very nice), but you'll need the mic as well, which bumps the price, but as I said before, it's ProTools...
The above suggestions will give you good sounding, controllable audio with a USB connection, the easy way is the M-box and mic, but it's also the most expensive (I don't know how much the M-box is in the US) and you get a great audio recorder that imports video, the mic/pre-amp and converter is probably a little cheaper, but you'd need to brush up on your recording technique (not by much) and you'll need an app to record into.
Hope this helps, let me know if there's anything else.