Possible Temporary Mac Workaround
This worked for me during testing so I believe it may work for now too.
First off, download Tekkit and set it to the most up to date version..log in and all that so it downloads everything.
Then go to the Tekkit mods folder where you normally would put the extra_mods.zip contents and delete everything.
Now download the LinkTart launcher and extract it. Copy the contents of the mod folder within there to the Tekkit mod folder.
I *think* this worked for me (on PC admittedly) when I was testing yesterday...so..give it a go
Thanks dude Will give it a try after work