Funny that you mention the DLG files since I was just playing with them. I found that they had water detail in my area for just about every quad, and when I overlaid it on the NHD data, it matched perfectly. I compared a couple quads with which I'm familiar pretty carefully and even the little streams matched. So I got all excited because they are really quick and easy to download. Then, after collecting a bunch, I looked more carefully and leaned that none of the little streams or lakes were labeled, they just had some kind of ID number. Too much trouble...
I have used Macs since the very beginning and bought MacGPS Pro a a number of years ago. I stopped using it quite awhile ago and never upgraded so I don't know what's new. But realize, they cannot send MAPS to your GPS (unless it's a very new feature!). The raster imagery is only for viewing on your computer. Newer Garmin models (Dakota/Oregon/Colorado) can use raster imagery that you make yourself, but not the 60csx. Personally, I don't find MacGPS Pro useful anymore. Mapping is one of those fields where the Mac is WAY behind - and I do mean WAY behind - the PC. For a variety of reasons, I don't think that will change anytime soon, and that's a shame.
But the good news is, you can install Windows and run the powerful PC applications right on your Mac. Now for ordinary stuff, like loading map files on your GPS and using Garmin's own products, the Mac versions of Basecamp, Roadtrip and Mapinstall will work fine on your Mac. But if you want to MAKE your own maps, then that's a problem with the Mac.