again by going from an interview I read of Chris Tector some time ago, maybe a month or two, when he was asked about scorpio and if he got everything he wanted out of microsoft's new hardware, he had one "complaint" to do: he said he pushed for some dedicated sound h/w chips and stuff, and these did not fit the final bill of materials.
We have to keep in mind that Forza Motorsport having this strict recipe for max resolution-max framerate at all times, it must make their sound resource budget thinner than other titles. Under this perspective, sound design in FM is even more impressive. Especially if these sound improvements we saw on E3 reach xbone too.