Diffuser to fit Remus US race quad exhaust

So today I got my quad remus us race exhaust for my 2008 335i and I took it to an exhaust shop near and they said the diffuser( which was meant to fit the quad exhaust) wouldn't fit at all. I know you have to cut a few things and make adjustments but this diffuser's exit was matched up with the battery and would not fit.

Is there any recommendations for a good quality diffuser (carbon or plastic) that would fit my exhaust in a reasonable price range. I know I sound ignorant asking around and not doing any research but I want to see if anyone has experience with a similar setup.

Thanks in advance for any help.