What are the differences between the SVS PCi series and the PC Plus series other than the more powerful amp, adjustable subsonic filter, and tunable ports? Is the frequency response pretty much the same? Does the Plus have greater excursion, etc. I ask because I don't really need a fancy sub, I would just like a nice one that has the ability to be run quite hot (sadly, my DIY sub is not up to the task). However, if the PC Plus is clearly superior to the PCi, then I'm prepared to go for it. Also, just a miscellaneous question. It seems that the Ultra is very flat, but does not go as low as the CS/PC series. Is that correct? That's the impression I got from the charts shown on the site.