I use the art unit with it's converters going into the spdif of my firepod. It's my cheapo great sounding sleeper coloring preamp for vocals and guitars and solo instruments. Nobody knows it's what I'm using, I have a very broken neve as well and someone assumed I was using it when they heard the sound of their vocals (a mature, experienced studio recording jazz singer) and loved the tone. This with a rented u47 and one channel of the ART preamp, using the ART's converters.
I have to completely disagree about the art's converters - to my ears they're excellent. I'm not comparing them to the analog outs, that's an apples to oranges comparison (although certainly valid if you get the sound you want using the analog outs). I did comparisons with a digi 002, my firepod, an fa-66 (converting at 192khz, just for comparison), and the art. The converters in the firepod were pretty much on a tie with the digi, maybe even slightly warmer than the digi.
the fa-66 is so bloody transparent at 192, but when brought down to 96 like the rest of the converters it definitely took away a speck of 3d depth, and the art had the most 3d depth and spaciousness of them all, micing stereo pairs with it of a string quartet produced amazing stereo realism, noticeably more so than with the digi or even with the firepod. So I use the firepod for most trackign but the art for vital lead vocals and instruments, especially for classical work.
Hope that's helpful. Never used the rnp though have heard good things about it. I've used some insanely expensive older studio units, and the art doesn't have that distinctive character of many of those units, but it's great for the money and gets you in the right direction. A good quality mid grade unit, like a firepod. Definitely worthy of pro studio work if you don't have $30,000 to kill on pres and converters....
Cheers,
Don