Cat 5 has not one advantage as far as install is concerned as far as I can see, there is the argument for balanced digital, which may or may not help? But I didn't find plugging a din and a phono in when I set up my speakers particularly stressful, extremely time consuming and I certainly didn't think 'if only this was on a single plug I would have been so much happier."
Problem for me is I have less and less need for a processor these days as I am now ripping cds and sticking them away, every thing is via a server, so at last the Meridian DSP speaker with digital inputs is all I need for a stereo system, but without an coaxial in it gets messy.
Airport express - DSP speaker. Job done at a just a bout doable price for the office/kitchen/bedroom.
Airport express - controller - DSP speaker. Too expensive for the office/kitchen/bedroom.
Not for many I am sure, but although I earn good money I never seem to have any left at the end of the month, certainly not enough to waste it on unnecessary pieces just to get it up and running.