I recently bought a used pair of Martin Logan Aerius 4ohm speakers (my 1st pair of higher end speakers) as well as a brand new Rotel RSX-1056 (75watt x 7channels or 100watt x 2channels) surround receiver and Rotel DVD. I also bought a new Martin Logan Dynamo subwoofer. I am somewhat frustrated becuase when I turn up the volume to a loud (but not super loud level) the speakers start to sound like they are distorting with vocals on CD's. I am wondering if there is something, without spending a fortune, to make the speakers sound better, without distortion at a louder (more volume) level? Would an amp make a difference or have the speakers just reached their capacity with the current receiver I have?

Also, if there are any other recommendations other than an amp, please let me know! I am trying to learn as much as I can.