Not an apple guy so take this accordingly.  In general, music servers do not require a ton of horsepower.  The kind of performance increase he's talking about will likely go unnoticed.  If RAID is a technical issue, the other option is to still leave them separate, use the 2nd drive for music, but, have a folder or folders that simply have shortcuts to folders/files on the first drive so you can maximize drive space usage.
Bryan