Any sound difference between DB25 & RCA Connection

I have a Rotel 985MKII 5-channel amp and processor.The dealer recommended connecting the DB25 from amp to pro. for simplicity and savings from buying 5 sets of cables. He told me I wouldn't appreciate the difference in sound. Does anyon have any experience of comparing these 2 formats? Also, I have an Audioquest $50.00 toslink from DVD out to Processor Video4 input.I have upgraded PC's and speaker cables with much improvements but the sound, although clear and musical has a " glassy" sound to it, even on well-recorded CD's. My DVD doesn't have coax out, just analogue out and toslink.My speakers are B&W N804. Any recommendatins for improving the sound and eliminating the glassiness would be greatly appreciated.
I have the Krell HTS 7.1 with Krell amps. I inquired with Krell upon receiving the eqipment about using the DB25 connection. Basicly I was told that it's just for convienence, not for the best sound quality. So it really just depends on how much you want out of your equipment, and how much your willing to spend to get it. I am using Audioquest Anaconda Balanced interconnects ($1000.00/meter) and they sound wonderful (they should for what they cost), but what I mean to say is within reason you get what you pay for. I would say if you compared the DB-25 with a equally priced RCA cable there would be little difference. The problem is that you can only get a cheap quality DB-25 cable. Whereas the sky is the limit with RCA or Balanced cables. I would highly recommend that you forget the DB-25 and get the best RCA or Balanced cable you can afford. There are several on audiogon that are slightly used which are quite a bargin. I think for your system the best bargin and a very good cable is the Audioquest Viper. I just saw some on audiogon for about $100/ pair. That's a very good cable, and I'm certain you would hear a noticable difference. Let me know if you have any other questions.
Thank you Simancd for your thoughtful suggestions.I will definitely begin pursuing some good quality RCA interconnects.