Hi slick. Gosh I don't have any first hand experience with the Imagine center speaker or the Image center for that matter. The common recommendation is to stick within the same model line for L-C-R speakers and I think for the majority of applications this is sound advice. I don't think your sound stage will be shot to hell by mixing and matching but I also don't think you'll be gaining much with the Imagine center. I'm a 2 channel stereo guy so maybe someone else can chime in and see if I'm on track with that.
I think a set up 3 Images across the front with your SVS sub will be a competent, enjoyable system.