I recently spoke to the company about the noise issue prior to purchasing my first Mokai (I have not yet received it). It's my understanding that the custom tuned muffler provided for the Subaru has a more quality sound that is less "tinny" than the one that came with the Honda.
I asked about the decibel level of either the Honda or the Subaru and was told that neither is available at this time, but plans are to get these measurements as soon as weather and time allows and to post them on the company website.
Also, a new mufflers is being considered that will reduce the noise even further. However, it will most likely also reduce the engine's power. If a significant noise reduction can be obtained without an objectionable loss of power, this muffler will be made available as an option.
As I understand it, muffler changes involve retesting by/for the EPA and this is a time consuming operation. This new muffler option could be several months away and MAY not happen at all.
Again, this is just my understanding from the conversation. Sometimes I read between the lines things that are not there at all or just flat misunderstand completely. Contact the company if you have any questions or need to hear it from the horse's mouth.