http://www.rdlnet.com/rusx4a.htm
http://www.bswonline.com/public/sear...cat=interf-swi
Ignore my note below. Didn't know the EAR HP4 was a balanced model. Those must sound real sweet. You will need professional broadcast devices to satisfy your requirement. Look at the RDL model listed here.
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It really depends on what you are planning to do source switching on. Here's a short summary that I am aware of - is this what you're referring to? Are you switching analog and/or digital audio? Video? Both? Since this is a headphone forum, I am assuming you just need the audio portion.
Audio Switching
1. Analog - L/R RCA jacks
2. Digital - choice of switching
Optical - using TOSLINK fiberoptic cables
Coax/SPDIF - using digital coaxial
Video Switching
*Video
Composite/RCA - RCA
S-Video - 75 ohm S-video cable
Component Video (Y, Cb, Cr)
BNC connectors
VGA
Some sites to go to -
Audio Authority, Key Digital Systems, Extron, etc,