Sorry to tell you, but you don't have 200 watts now (see manual at link below).
http://www.yorkville.com/downloads/manuals/ombm200.pdf
The amp is rated at 150 watts at 4 ohms (the stock 15" is 4 ohms) and 184 watts at 2 ohms. Adding the 4 ohm Eden cabnet will lower the impedance and you should get a few more watts, but you probably won't hear the difference between 150 and 184 watts. You'd need to double the power to get a 3dB gain in volume, all other things being equal. Having said that, what a given speaker does with that power is a whole 'nother kettle of fish. The efficency (or lack thereof) will make a big difference in the volume of sound as perceived by your ears.
Having said all that, I have a Yorkville BM200 and it's a great combo amp. As with all combo amps with a 15, it's a bit farty on the low B if you play a fiver, but for small gigs it's perfect. Nice, not too big or heavy, and sounds pretty darn good.
