I would just do Mac. But I know saying that is like standing up in the foxhole in a firefight... with sharp shooters.
If he or she doesn't need a lot of channels and if he/she wants REALLY immaculate stuff, this might be the one. Pristine sound:
Very high end mic pre and great converter in one box. But it IS for very high end stuff.
Here's a less expensive version of the same thing. Very high quality still. Runs on batteries. The ultimate in lightweight, affordable.
Actually, I would go with that one. $1525 and you can find it cheaper/negotiate. This is a good time to be buying audio stuff!
They make one with a Toslink/Lightpipe output! Same price. (Might need a toslink card for the computer??? Should be cheap)
Grace makes audiophile stuff. Resale value will hold much better than other stuff because of its rep.
I'm sure this will smoke any RME converters. And it's lighter, less bulky... and holds its value if not trashed.
They also have lightweight portable mic pres. All Grace stuff is very high end, transparent etc.
If he/she only wants to record one channel could go with one of the new Neumann mics with digital out. Save a lot of weight (no converter RME, Lunatec etc needed). Not cheap. I've never really looked into it, or how it interfaces, but it seems like a cool idea.
Here's some cool pencil style mics with interchangable heads from the guy who created Royer Mic's. Could find 'em cheaper
They're a bit cheaper than the KM 184. I have a pair of KM 184 and like them okay. Great for banjo.
These are decent. Used on many big recordings.
My experience, and a lot of other folks' experience, is that the microphones are so important if you're doing acoustic recording. In fact, I'm amazed at the difference. At first it seems maybe subtle, but when you start mixing lots of mic'd elements together the quality really starts to shine through. They just blend better. Less crud.
I'd spend my money on a good mic and mic pre. I think the Grace Lunatek, a couple nice mic's, maybe a Toslink card... and you're set to record very high quality stuff. But then, if you're recording heavily processed music then it could be a different story.
The Chinese and Russian mics can be VERY good. But you need to buy them through one of those guys that sorts through them and weeds out the dogs. I'll try to remember the name of the one company I heard of that did that.
He should check out the videos with that guy who traveled around the world and did recordings of different folks working on the peace song. Can't remember his name right now but saw a good documentary on him talking about portable recording. I'll try to remember where I saw it. Could have been through Mix Magazine (www.mixonline.com) or electronic musician online.
Come on down to NAMM and we can look together! But I'm not there on the weekend