So after some consideration to the several different exhausts we can use on the NM4 (yes, all of the NC700x exhausts I've tested will fit just fine using a slight modification to the hangers) I ended up with the least expensive, and in my opinion, best sounding silencer/muffler I have heard.
I was looking for something very throaty which provided a boost in sound but wasn't overbearing. I didn't bother with the Moriwaki simply because I didn't want to spend $1K on a muffler. I lucked out while Roy was around in that he had several NC700 models come through his garage and would record the audibles, with a couple of weekends where we were able to put a few on the bike and listen to them (and we didn't have to force them on or adjust the pipe to fit them in place). All were louder than stock, but only one was kinda close to the tone I was looking for. Roy tried his hand at using 3 smaller coned pipes in an N configuration within a triangle-ish shape to fit under the pannier but it ended up sounding like pissed off bumble bees in a folgers coffee can. We pretty much kept looking for off the shelf stuff at that point before he ended up leaving Austin for work.
I dropped by Revival Cycles here in Austin and talked to Chris who looked at a CAD design I presented thinking that a dual warped cone to a 2 inch set of pipes would sound great...he let me hear a couple of the longer cones on some of the ducati's then we talked about dropping on a shorty cone to open the backend up like the other side by essentially tucking and hiding the cone a bit.
Since they were too busy to get to it, I ordered the cone and did a temporary propane solder job making a stainless ring with flux and solder. The 12 inch cone is from Cone Engineering purchased through moto-madness.com. It not only sounds awesome, but I couldn't argue with the fact that it was stainless steel so it wouldn't rust out, AND it was only a hair over $100.00.
To listen to it, hit my youtube link:
The original exhaust sound from the first day recording: Original Exhaust Sound
The Cone Engineering 12inch Shorty recorded earlier tonight:Shorty Exhaust Sound
Here is a link to the website I purchased the silencer from, if you do go with this, you want the 1.5in unit. It literally slides right on to the existing pipe. You can then integrate it with screws, a clamp ring (by cutting the end so it collapses), welding it, or soldering (which is easily removed by applying heat back to it and pulling the cone off). The exhaust is extremely light by comparison to the original so you are shaving somewhere around 6 lbs off, possibly more.
Moto Madness Cone Engineering Exhaust Page
The next project is to get it tucked up a little higher and closer to the body, then hide it with a shield that covers all but the end of the cone so you would have to look twice to notice there was an exhaust outlet there. It also throws the exhaust out to the side but another plan is to weld a flow plate on it to guide the exhaust downward to keep it from damaging or sooting up the plastics.