All patches sound similar.
Do you mean that there is some type of distortion or defect to the sound that is heard on all of the patches, or do you mean that all the patches sound like each other?
You probably need to be more specific about what does not sound right about the synths. Since the different synths are quite different programs, anything that is affecting all of them must be in their interaction with the host program (Sonar), unless what you are hearing is due to dropouts from insufficient processing resources. You might be clipping, squashing with compression, or filtering etc. etc. but who can guess without a better explanation.
It would be nice if this forum had the capability to upload audio files, but lacking that a better explanation of what you are doing and what you are hearing would help. Taking the time to write a detailed explanation of your problem is the first step in getting help.