Dan - the point Marc is trying to make is that Nashville demos are played by the same people who are playing on the records when they're released. If you have someone who is not playing on the records when they're released play on your demo then they will not have the same style, tone and feel as the other demos, and will be rejected because "they just don't sound right."

Someone had a post a while ago about "the wrecking crew" which was a small group of guys in the 50s and 60s who played on basically every hit record by every artist. From what I understand its the same thing today - the same players playing every song. These guys do demos too and if you choose not to use them then you're at a disadvantage against the other thousands of songs being pitched.

You can make a GREAT studio at home, but its the people playing on the records that make the difference, not the studio itself.