Yeah, not many makers offer a muffler that short, it has to be around 11-12" and most are usually 14"-up.

I recall Borla has one in the racing muffler section of their catalog.

You can use a cannister muffler tilted a bit. Someone online posted pics of Magnaflow cannisters mounted that way on his 3.0 X5.

As I posted in your first thread, have you looked into putting on 4.6/4.8is OE mufflers on? Quite a few here have done it and are happy with them.

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04 X5 3.0i auto
03 X5 4.6is