Lack of bass was a deal breaker for me on the SS too. I didn't want to have to lug around a sub with it.
I did find out last week that the PA4X loses something when summed to mono. Not as much as the Yamaha loses, but still, the sounds that are designed to use stereo effects suffered somewhat in mono when I was without one of my Maui 5s for a week. I had to change my default piano sound. I didn't realize how much until I hooked back up in my normal configuration!