There's no need to save the XT files as CSV files. You can directly import the XT files written in ARC XT, into ARC 536.
Start ARC536. Go to File>Import. Clicking on Import opens another window. Click on the line that says "Import ARC XT File". Then navigate to the location on your computer where your ARC XT files are located - they have .rsf file extensions. Click on the file you wish to import. The data will appear in the ARC536 Browser. Most of the data is there (frequencies, Alpha Tags, squelch tones, NAC and sites for trunked systems).
Since Service Type is something new in the 536 programming as compared to the XT, you'll have to edit the Service Types in ARC 536. I've also found that GPS data does not import, so if you do GPS scanning, you'll have to enter that.