good luck,
I don't think you are going to find anything with S/pdif and dithering for under $1000. Maybe you need to start thinking used. Also, would your $1000 be better spent at a mastering house or on a mastering processor?
This is not intended as an insult but, you do know that mastering is an art form, right? Buying a mastering box is only going to start you down the Yellow Brick Road, it's not going to get you to the Emerald City.
Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com