If we just use the copyright symbol can that be used as legal copyright?

The symbol is not enough. You must also identify the copyright year and holder, for example
Copyright ©2008 by Your Name. All rights reserved.

It is also good for business if you add a contact email for people who might want to do something with the work.

It sounds like you haven't actually copyrighted your music, you're just putting the symbol on your CDs. If this is the case, you can use the symbol, but if someone else registers your music with the U.S. Copyright Office, you have no legal recourse whatsoever. They own the rights. You can show original sheet music, signed dated and notarized, but it won't stand up in a U.S. court of law because you didn't register it with the U.S. Copyright Office. If your music is that good, protect it. $35 per song is a small down payment if you think your material is worth millions. Go to www.copyright.gov and do it right.