I believe tube rolling can make a big difference in the sound of the component. Whether or not rolling the originals out of the Migda will be better or not, only you can decide.
I've had great luck with sellers here on A-Gon, as well as Jim McShane (google, you'll find him). Jim will help you get the right tubes for your amp and your preferences.
Personally, I would recommend you begin with the 12AU and 12AX tubes. Cheaper, and my experience has been that they affect the sound more (certainly as much) as the output tubes.
Have fun!
I've had great luck with sellers here on A-Gon, as well as Jim McShane (google, you'll find him). Jim will help you get the right tubes for your amp and your preferences.
Personally, I would recommend you begin with the 12AU and 12AX tubes. Cheaper, and my experience has been that they affect the sound more (certainly as much) as the output tubes.
Have fun!