You will not see a difference in video and there will be no better sound. The only reason to switch to HDMI in your case would be if you need to free up a digital audio connection for your surround sound receiver. You can use either digital coax or optical cables for your audio if you have either connection available. The sound quality with either of these will be the same.
I know there are technical differences and some will point out the differences. In reality, you will not actually be able to see or hear it.
Sony SXRD KDS50A2000 TV that has 2 HDMI IN connections.
Harmon Kardon AVR520 receiver (No HDMI)
Pioneer DV-250 DVD Player (No HDMI)
Dish ViP622 DVR (1 HDMI OUT)
Dish VIP622 into AVR via Component(Y,Pb,Pr) for video and Optical for audio.
Pioneer DVD into AVR via Component(Y,Pb,Pr) for video and Optical for audio.
AVR into TV via Component(Y,Pb,Pr) for video
Can I or should I use HDMI from my Dish DVR into the HDMI on the TV and then use the Optical Out on my TV back into by AVR Receiver or do I have to have HDMI on a receiver to take advantage of it? Or What would be the best connections for sound and video? What will give me the best video and sound?