I don't have nor have I heard the combinations you are comparing but I can reflect on an experience I went through, maybe it can provide some insights for you.
I have an M&K 150 setup with the M&K 350 sub as a replacement for the 150 and an SVS 25-31pci sub. The 350 sub is a higher end 150 and costs twice as much while the SVS sub is in the $500 range.
I started with the SVS sub and added the M&K combination later. in my opinion, the SVS sub gives more bang for the buck at the lower end of the spectrum. However, I believe in matched sets, especially with satellite systems (i.e., the matched sub is designed properly to fill-in where the satellites leave off). Thus, I bought the M&K sub even at its much higher price tag then the SVS.
How does this relate to you, you say. Well I like the performance of the M&K sub with M&K satellites. However, when it comes to bang for the buck in an area where home theaters like it (low bass). I side with companies like SVS and HSU which are highly thought of on the forum for providing deep bass at a reasonable price. Since neither sub is specifically designed for your other speakers, it is my opinion that you should go for the combination that will give the most obvious improvement to your movie watching experience (i.e., HSU or SVS).
A forum community dedicated to home theater owners and enthusiasts. Come join the discussion about home audio/video, TVs, projectors, screens, receivers, speakers, projects, DIY’s, product reviews, accessories, classifieds, and more!