I have just got hold of an acoustic image contra in England. I am impressed by its sound at lower volume levels but disappointed by its volume level and headroom, it doesn't seem to want to go very loud before starting to sound a bit strained. It obviously needs an extension to help it out and Ive tried experimenting with anything that came to hand. Any existing bass cabs I had around were disappointing in that they lost the natural sound of the contra. However the thing that sounded surprisingly good were some PA speakers I had. These were a pair of 8 ohm EV S200s. I tried one as an extension and it sounded good. I then wondered about getting a 4 ohm load to give maximum power. I then realised that if I connected the second EV to the output socket of the first it was parallelling them up and creating a nice 4 ohm load for the contra ( I checked the impedance with a multimeter to make sure). This really seemed to allow me to run the contra hard and gave a significant volume increase. I was wondering: 1/ If I am likely to cause problems for the speakers in terms of cone extension etc. given that they are not designed for bass (but they are rated at 300 watts continuous each and I'm using 2 connected together into the extension socket of the contra). 2/ If my assumptions about power into each speaker was correct. I was reckoning that on full whack the contra would be pushing 150 watts into its own internal speaker and 150 watts into my PA speakers, which presumably means 75 watts each. 3/ If I do overdo it in terms of power or cone extension, will I be able to hear it in terms of degraded sound quality before causing damage?