I could never get the imaging right with the RTA-12Cs... somehow, the Monitor 10s seem a bit more focused. Well, I decided to replace the Marantz PM7200 amp with an Onkyo TX-905 receiver since my wife wants to listen to FM.
The Onkyo was used with my big screen which was upgraded to the TX-NR906. The speakers of choice there is the well regarded Sony SS-M9s which some may know was designed by ex-Polk speaker designer Dan Anagnos. He was with Polk during 1984-1992, Sony 1992-2002, Boston Acoustics and currently the VP of DM Holdings. The Onkyo sounded fab with the Sony speakers. Imaging was first rate with excellent sound and depth.
When I hooked the Onkyo with the Polk RTA-12Cs, I was surprised at how the soundfield collapsed. Left to right was merely okay and depth was unexceptional. I swapped out the IEC power cable to a 14G from 18 and there was some increase in depth. Just for the hell of it, i swapped the Polks around, left to right and vice versa.
That made a BIG difference. Just to double-check, I looked at the label to make sure that the speakers were in the wrong location. But there was no mistake. The soundfield was far superior when the speakers were moved. Normally, the full range midwoofer would be on the "inside" of the two and now they were the "outside" pair. Any RTA-12 owners should try it and see if it makes a difference to them too.