"We hope to have this resolved in the next 24 hours and apologize profusely for the delay," wrote community manager Sean Baptiste. "Again, we apologize for the delay and are working our butts off to get the content out to you."
On its official forum, the studio noted that download codes for Xbox 360 owners began going out last night, but that "due to the volume of emails being sent, these will roll out over a 24 hour period." Harmonix also stressed its appreciation of your patience.
Despite Harmonix's claim that the codes began going out last night, it appears that the codes have not yet started shipping out, as no one has yet reported their receipt.
Meanwhile, PlayStation 3 owners will start to receive their codes later this week, when the online PlayStation Store starts carrying the tunes on Thursday.
Harmonix has yet to detail when the tunes and other DLC will be available to those that buy the Wii edition of Rock Band 2 after it arrives in December.