Rhythmic F12SE setup using line in

Well, regardless of the online instructions it sounds like either your crossover is set too high or the volume is set too high, or both. So I’d first play with turning those two settings down first and see what that does, and then try altering the phase to see if that can improve things further. The other thought is that your sub is not placed optimally in your room that the prior room correction software was compensating for, so you may need to experiment with sub placement in addition to adjusting the sub’s controls. Here are two helpful links to address both issues I recently posted on another thread that may be helpful for you too…

First, if you haven’t already, use the “crawl method” to find the best location(s) for the sub(s) in your room for best bass…
https://www.audioholics.com/home-theater-connection/crawling-for-bass-subwoofer-placement

Then use this to fine tune your sub’s individual controls…
https://lifehacker.com/how-to-properly-set-your-subwoofers-volume-without-sh-1506136549

Using these techniques should give you a high degree of confidence that your subs are dialed in well. Hope this helps, and best of luck.

I believe that your Marantz along with the Audyssey was performing both low and high pass functions and some e.q. functions. If you are unable to incorporate the Audyssey into your current setup you no longer have any of their benifets I.e. clear. Concise, crisp bass. The only function of the three that you have left is the low pass filter on the Rythmik.

The muddy issue comes from setting the low pass filter too high. Since the KEF’s have a -6 db point at 30 Hz. Start by plugging any bass ports the KEF’s may have and then set the Rythmiks low pas filter at 30 Hz. You can then make small adjustments in the crossover point until you achieve the sound you like best.

If your preamp is a stand alone unit, you could purchase an outboard crossover such as a miniDSP, which I believe is compatible with Audyssey and very closely recreate the the same set-up you had with the Marantz.

Low, High, or Mid for your dampening? Also, are you engaging PEQ?

High dampening. There is not a PEQ unique knob. The nonLFE switch setting is 50Hz/24. My only other option is 80Hz/24. I believe the crossover max and rolloff. 

@audiorusty 

Interesting recommendation. The KEF’s do come with plugs for the rear ports. I will give that a try, while reducing the crossover. Had a similar recommendation from @soix Thanks!