Sonos - Optical or Coax or RCA out?

Amp - Peachtree Nova
Speakers - Zu Druids

I have a computer based system (listen to MP3) and I'm looking to incorporate a Sonos ZP90. Should I use the Optical, Coax or Analog RCA out to the Peachtree? Also, what type of cable would you recommend and what length? The Sonos will be stored inside the Peachtree and only requires a very short cable, however I have heard that a longer cable may be better.

To take advantage of the Nova's internal DAC (which some say is the best part of the Nova), you need to use a digital input. There is a general consensus that COAX -all things being equal- is better than Optical, but it may still depend on your source (computer based?). Did you consider USB?
Most often recommended length of digital COAX cable is 1.5 meters if you decide to go that route. There are many great cables out there, do a search on the topic.
You can connect the Peachtree directly to your PC via USB if proximity allows. If the Peachtree is setup in another area then the Sonos is a great product and I agree with Arni's suggestion of the coax cable interconnect.

This will be a nice setup but I feel MP3 will not do it justice. Try some lossless audio (16-bit/44.1 kHz) and you will hear a big improvement. Move up to 24-bit/96 kHz for an even bigger improvement (from your PC as Sonos does not support 24/96). Once you have listened to some high resolution audio you will really appreciate the Peachtree.

Whatever cable you choose will have less impact than your source material's resolution and bit rate.
Get a few different cables and compare. Coax usually sounds better, but there's an exception to every rule.

If contemplating optical, I bought a Sonicwave glass optical from Amazon for about $25 shipped. Sounds fantastic! For the money, it's easily worth the risk IMO. Just don't bend glass optical cables very much. You shouldn't sharply bend any cable, but glass is obviously more easy to damage.
Thanks for the feedback. My peachtree, computer and modem are all in different locations in the house. I have a NAS and I will have a zonebridge br100 on my modem and a zp90 in my peachtree. I hope to get the NAS setup to work. Are there any limitations with this setup that I should be aware of? Unfortunately, it sounds like USB is not possible.
I did an A/B comparison with the optical and COAX on the ZP90. Aside from impedance changes and volume, they sounded very very similar. But I did note a sharper and less rolled-off sound with the optical. Due to my setup I had to put the optical on the PS3 and the COAX back on the Sonos since my Cary DAC only has one of each. And of course, each rig will sound a bit different with all the variables... of course! But coming from a Sonos? It's not exactly the most demanding hi-end piece of gear out there.

I put a $200 digital COAX on there vs. an $80 optical. I'd have kept the optical if I had the option and it's not because of price. It really sounded just a touch cleaner. That's all. You would not know the difference if someone changed out your cables over night and you listened to it the following day.

And limitations? Not really. There are debates over using CAT6 vs. CAT5e and so on but another improvement I had was when I replaced all the CAT5e cables with shorter CAT6 patch cables. The bass was more pronounced and very clean and tight. I was like, wow. Who knew? Again, cables are hit and miss in about every system. But the CAT6 patch cables are cheap and readily available and I consider any addition that is overkill is the addition I have to worry about upgrading or changing last. I'll never have to wonder if they are limiting my system because as of right now, the Sonos is far from capable of putting out that kind of bandwidth.

Good luck!