That's a real bummer that BMW have withdrawn it. It's the go-to option for improving the straight-six exhaust sound. I'm sure I've read that Eisenmann actually manufacture the PE, so I don't think you'll go far wrong with them.
Also worth keeping you eye on the classified section on this forum, as they do occasionally pop up when someone's de-modding their car before sale...
P.S. When I was looking into an exhaust for mine, I did also consider this:
https://www.corsaperformance.com/col...xle-back-14564
Although it's for the 135i, it's for a single pipe system and I think it would fit your car. Oh and another option to consider is Supersprint:
https://www.supersprint.com/ww-en/sp...engine-07.aspx