Frank - here is where things get tricky. It all comes down to the word "core". Basically, a S/PDIF connection is bandwidth limited and cannot pass full uncompressed audio. Dolby TrueHD is uncompressed audio. Built within this signal is a "core" dolby digital compressed audio stream that CAN be passed via S/PDIF - this was a requirement of the new audio formats so that they could be backwards compatible with older receivers etc. What IS true is that while this signal is indeed compressed, it is at a higher bitrate than what is found on sd-dvds thanks to greater disc storage capacity.
To listen to the uncompressed TrueHD signal, you need either 5.1 analog inputs or HDMI, both of which have the bandwidth necessary to carry the audio stream. If you compare the "core" stream with the uncompressed stream, you will definitely notice that the later has far more clarity, impact, depth and subtlety. It has nothing to do with having a 5.1 audio system as opposed to 7.1 - it has to do with bandwidth, connector type and audio compression.