CHDK for A590IS and RAW processing
Not sure if there are many who have your model and also want to avoid CHDK's DNG conversion. You don't mention your version of RT:
I've been using v4 beta without any problems. You'll see you have a choice of demosaicizing algorithms in whichever RT. I can't say more than the obvious of trying them out against the same shot taken with the in camera DNG conversion in your model. You can also preset WB, sharpening and other basics for all your conversions in RT.
I've found the in-camera DNG conversion only adds incrementally to the much longer delay for the CHDK RAW process. DNG doesn't change my use of CHDK RAW - I either have time for it or not between shots - and it adds greatly to the availability of software.