But if it works using Toast then it's not that big of a deal.
Encore has never been the best "burner." Many of us on the PC side use imgburn instead. I have no idea how Encore burns beyond CS3!
But there is no reason, based on your results so far, not to use Encore to author. It may work great for you.
Think of 3 separate stages:
1) Exporting from Premiere, another application, or using dynamic link. The huge advantage when DL works is that you can move back and forth between your Premiere project and Encore without having exported first. Also, you can use the "automatic" transcode setting to max quality. When exporting from other apps, you must get the export to DVD specs and you must transcode to the correct bitrates to max quality on your disk. You can also export a lossless intermediate and bring that into Encore for the transcoding to be done there.
2) Authoring in Encore - menus, navigation, etc. You can import the assets from any export system or dynamic link. But Encore (being build on the sonic/roxio authorcore) is very picky about assets being to DVD spec, and will retranscode anything that isn't.
3) Burning. Encore has the options, but you can also build to an iso image or DVD folder, and use that to burn in another app.