Coaxial or Optical

I am just getting my new HT system together. It includes an Onkyo 676 (old Adcom seperates for Stereo), Pioneer Elite DV-37, and NHT 2.3A's and matching center and surrounds. Should I use coaxial or optical to connect the DVD to the receiver? Does it make a difference? How much do I need to spend that will make a difference? I am using an 8 year old Sony 32" XBR. For video, I only have S video, can I connect to the receiver first and then to the TV? Does this degrade the signal. I should have it up tomorrow. Any input will be really appreciated.
Oh no ... I think you're opening the "thread from hell" asking about how much to spend on interconnects, Pablo. With no intent to sound rude, I really suggest you search out the archives here and read up. At the very least, you'll get a feeling for the multitude of views on this subject, even if you never do quite get an answer. Some of it does make for interesting reading ... at least the first couple hundred times.
To answer your question about spending more for interconnects, that depends. I wish there were an easy answer but $$$ does not necessary equate to quality. To give an example. Not too long ago I auditioned 9 or 10 power cords ranging in price from $70 - $600. The $290 Custom Power Cord Model 11 bested them all when used on my power amp. On digital sources the $600 Marigo Ultra Series II was the king of those auditioned. But the $70 Stealth HAC came in third, well ahead of the $500 JPS Labs. To make things even more confusing, someone else will likely get different results on their equipment. So, the answer to your question will have to come from you. Many manufacturers have 30-day money back garrauntees. You can also borrow cables from the The Cable Company's Library. Decide what your budget is, make a list of several cables you are interested in, and start auditioning. My recommendation is that you not try to audition more than three cables in any given three or four week period.
About 6 years ago I belonged to the "bits is bits" camp, and thought that interconnects couldn't possible matter. One weekend I brought home a Wadia dac from my dealer to try. He loaned me a $200 piece of coax to use, which I politely accepted without laughing.

When I hooked up the dac, I used Toslink from my Sony X77 CD player out of convenience. I already had a Toslink cable plugged in and the back of the player was hard to reach.

I was unimpressed with the dac. Before I brought it back, I decided to try the expensive coax just to appease my dealer.

The difference was unbelievable. The soundstage opened up, low level detail appeared, and I couldn't stop listening!

Moral of the story: I avoid Toslink whenever possible.
Firstly, it is difficult to give absolute advice here because your dvd player and receiver will affect the results. Secondly, your budget is also a factor. If you only want to spend say $40, then you cou could get a Monster Lightspeed 100 toslink or Apogee Coaxial, get decent results, but the difference between the two will probably not be very significant. However, if you're willing to spend around $100 or more, something the Harmonic Technology or Madrigal or Illuminations, etc., will probably give you better results than a toslink, depending on your transport and dac.
O.K., Now for a more technical understanding of why there is not a concensous af toslink vs. coaxial connections. Although most of the time the coax connect sounds better, sometimes the toslink will be the better connect. How can this be? Because each manufacturer is using a different input reciever chipset, which is the real determining factor to which connection will sound better. (The input reciever is the chipset that "recieves" the initial digital data, and then passes this data to the D/A and other processing chipsets ). If the input reciever has a high immunity to jitter, then it usually sounds best with an optical input. Unfortunately, these type of input recievers have only been available in the last 18 months, and are most likely on a processing unit that employs 24bit sigma delta dacs. Otherwise with the other types of input reciever chipsets, the coax sounds much better. Don't even try to ask your manufacturer about his digital designer's input chipset reciever choice. He will probably mislead you, since many are totaly oblivious of the above aformentioned information. As a former sales representative of these types of chipsets myself, many processer and reciever manufacturers "swap out" and change their receiver chipsets, during the production cycle for both cost and supply considerations. They can make this change because there are many pin for pin compatible digital chipsets offered by competing digital chipset manufacturers. As usual, the best way to determine which connection is better is to do an A/B comparison between connection types.