<font color='#0000FF'>I am new to DVD-A and SACD. I have been researching to purchase an AMP. My mind is almost set to the Denon AVR-5803. This receiver has a RJ45 connection, it's the type of connections used in LANs (local area networks), so if I get a Denon DVD player that supports DVD-A and SACD, you can interconnect them through the RJ45 to get a digital link, one problem is it doesn't decode encrypted or copy right data, not until reticently that I read that the Denon got the approval or license agreement to play copy rights through it's digital link. Although the Denon 5803 has the Bass Management option on the analog inputs. Most of the other manufacturers also has digital links like FireWire to interconnect there own products.
FireWire can transfer up to 400Mbps (Mega bits per second), while RJ45 Connection used to transfer 10Mbps in its early stages, the 100Mbps, and recently supports Giga transfers, 1 Gbps = 1024 Mbps. While through an optical cable you can transfer Giga bits also, I really don't know why they complicate things. The RS232 data link for upgrading a processor's software is very popular, although not suitable to transfer digital A/V data as it is very slow, only for upgrades and Home Theater Remote Controls interconnects.
The Sunfire lets you upgrade it's software through data water marked on a CD, you play the CD and by the end of the track you're component is upgraded, so again, I don't know why they complicate things in the first place.
I am an I.T. (Information Technology) guy, been a fan of home theaters for 8 years but never been more into it than the last few months when I decided to upgrade my system, most of my pure technical information I got it from Audioholics Articles and manufacturers' websites. The data transfer rates above are approximates to my best knowledge you might have to confirm them if it's critical to you.
Note: I do post here for whatever help it could do, and for others to correct me.</font>