Special digital cable needed?

I just bougth a secondhand Yamaha DSP-E800 DD/DTS/Prologic decoder with built-in amps for centre and rear speakers. So I wanted to hook up my DVD-player, using a 75-ohm cable to feed the digital input on the Yamaha. Since the shop didn't have a digital cable and I didn't want to wait to play with my new toy, I just used an old analogue cable. And it works. And it sounds pretty good too. So my question is: will replacing this cable with a 75 ohm digital cable sound better? Or can I save the money and waste it on other joys of life?
There are no guarantees. A digital-specific cable could sound better -- or worse. If you have achieved a good result with what you have, I'd leave well-enough alone.

Some analog cables I've tried as digital cables have sounded better than digital-specific cables.
I asked Frank Van Alstine if a 75-ohm digital cable was needed to connect from the digital out on a CD or DVD player to the digital in on a OmegaStar DAC. He said "All you need is any old shielded cable with RCA plugs on both ends. The cable impedance won't matter unless you have a long long (>20 feet) cable run".
When I had a pair of leftover, earlier generation, Mapleshade analog interconnects, it was suggested by Pierre Spey that this particular analog design could be re-directed for use as digital interconnect, based upon his listening tests. Upon actually trying one from CD transport to Genesis Digital lens, and the second from Digital Lens to DAC, there was fine performance, comparable to the previous "digital" interconnects. Pierre Spey's product catalog is replete with comments about how his products are designed by listening to their results, rather than solely depending upon conventional wisdom.
As Plato explained above, you'll never know until you try.
The 75-ohm value is a "standard" of sorts. Basically, the reason for it is to keep the impedance between sources at a value where there is no signal reflection (which can cause jitter). Whether or not a 75-ohm cable sounds better because of it I guess depends on the equipment. If the equipment is in the SOTA category - maybe. If they aren't - maybe, maybe not. I'm sure cable literature will give you more details and reasons to buy "digital" IC's. But avoiding damage will not be one of them.
75 ohms characteristic impedance is beneficial, but not necessary. If you want to minimize jitter, then stick with 75 ohms and get a 1.5m length minimum. Ask someone with digital and transmission line experience for advice. Read this article I wrote on S/PDIF for more info:

Thanks for the responses, untill funds allow I just use the old analogue cable. Audioengr, just one question: why a minimum of 1.5 meter? With analogue cable should be as short as possible, and 0.5 meter would be sufficient.
Satch - this article I wrote for Positive-feedback explains it:
Thanx Steve, I read it and almost understood it - just let it digest for the night and I will be OK. Just for the record: I can lend a digital cable next week, and plug it in. I keep whatever sounds best......