I've only really experienced Bybees in a digital cable. I had Wayne from Bolder Cables build me a digital w/Bybees.

That's a pic of the very cable I own. The Cryo'd Napalm Ultra has 2 Bybees, full ERS wrap, Silver Eichmann Bullet Plugs, and Cryo treatment.
I've got a few of Wayne's regular digitals (Silver Bullet & Cryo only) as well as the Cryo'd Napalm Ultra. His regular cable was quite good on it's own. But the Bybee'd cable is easily better. I've not noticed any downside yet, and I've listened to my cable in my setup, as well as a few setups at VSAC two weeks ago (I brought it with me to the show).
I would certainly use a Bybee'd digital. It's a good way to improve the playback on all of your speakers, be it 5.1 or more (I'm running "7.2") for not too much $.
I do also have a Bybee S-Video adapter on hand that Wayne's loaned me. I've been burning it in for nearly 3 weeks. I've not had a chance to do A/B comparos with & w/out it yet. But I did watch a PAL DVD last night and used it at the input of my Video Standards Transcoder. It gave me better color & finer detail than I ever recall getting out of my Transcoder before. Hopefully sometime this weekend I'll have some time to do some real comparisons with it.