In case this may be of help to someone in the future:
I pursued the fact that the SS_SC(pin 9) select line for the waveshield remained low always. Even though this worked fine for the base waveshield code it was causing conflicts when combined with the Ethernetshield code.
After a lot of edits to the SDReader.cpp file I was able to get this to work.
I first started by commenting out the "card.partialBlockRead(true);" in the main file. This then allowed the SS_SC line to remain high unless actually reading a wavefile.
I refused to leave this commented out for some reason? I used the SD library>utility>Sd2Card.cpp as an example and edited multiple spots in the SDReader.cpp file to send "spiSSHigh"
when returning false. Lastly I then added a spiSSHigh prior to returning true when attempting to read data with a count = 0.
This got the SS_CS line freed up high after any wavefile read. However the line was still low just after init and before the first wavefile read. Something in the Fat partition reading. I was too burnt to pursue that one so I just forced pin 9 high after the partition search in setup and before the ethernet.begin.
**Success! ** Now the SS_CS remains high when not in use and the the Ethernet card works fine with the Waveshield. I am very happy after all this searching and editing as I admit I am far from an expert programmer. I am sure experts would handle this differently but at least this works.
Perhaps some people get it working right off after changing the pin used for the waveshield due to the SD card they are using ? (SD card dependent bugs in the code?)
The code hints at this by saying you can comment out the "card.partialBlockRead(true);" if you have problems. However I never had any problems with it uncommented when I was only using the waveshield. (no outward indication that there were issues).
Hope this may help someone else someday.