I've had success with a tool for the Mac called Foxit Video Converter that will convert the .m2ts stream to .ts. I think DVDFab will do this on the PC itself but I've been running off an expired (read: free) version that has the conversion features disabled.

I take it there's a reason why you don't simply use tsmuxer.

It all looks and sounds really good, but isn't the perfect-as-original stuff I've done with Womble and standard-def.

Have you experimented with M2TS cutters? There are a few available, and VideoRedo apparently has a smart rendering function. This is the only way that you're going to get the same results as you used to with Womble. Really though, re-encoding a Blu-ray with x264, especially with the higher quality settings, is extremely close to the source -- far more so than in the early days when people used to re-encode DVDs after editing. I don't think having to re-encode the video should be any kind of issue.