Probably a bit late with any info, but I'll confirm the 'NT' is New Technology and that a 60csx can use it - if you have the capacity on the sd card. Capacity isn't going to an issue with newer/larger sd cards - not all large cards will work with the csx - and the unit will damage some card, rendering it dead. Google knows about the problem
The NT makes use of a single really large file (>1gig) for all of the area covered; it is simple drag & drop to the gps'r. A downside is the copying time but once loaded you seldom need to re-copy - and the file can be copied to the sd chip using a faster sd port (either on a laptop or camera/phone) and then the sd is inserted to the unit. Garmin uses(used) a much slower than USB 1.0 protocol for the interface.
However, Mapsource seems to prefer its maps in smaller sections. For me, that required, breaking the big map into smaller, CNNANT 2011 (1,317,437,440 bytes) breaks into about 118 maps using MapSetToolKit.
I've loaded CNNANT and USTOPO100K and the Blue Charts onto a 4gig chip and had enough capacity to add a few other needed files.