Picking a speakers

Hey, I have run into this before. I have Soliloquy 7 channel speaker setup. A buddy of mine sold me a Sonus Faber Cremona speaker. I decided to replace my perfectly matching speaker with the Sonus Faber because it is 2x-3x as good. About 60-65% of the front sound comes out of the center speaker. It’s the most important speaker along with the subwoofer. You have to remember your surround processor has a ton of DSP. You would be amazed at how well it can match off branded speakers. Most important is to run your processor calibration software and then check your SPL’s on each speaker and maybe if you really want to dial it in to the last degree do some manual eq adjustments. One final note. My main theater speakers go down to 25hz and the center is 40 hz. Nothing gives your speaker’s position away more than bass or Hz below 80. I say if you have nice subs that can handle it cut them to 100-110 hz. If you have 2 way or 2.5 way-speakers this really makes sense because you will get much better mids since you speaker doesn’t have to work itself to death trying to get below 100 hz. Midrange is what makes sound real. In two channel mode I do full range with the subwoofer at about 60hz. I hope this helps. 

Thank you for advice

I’m familiar with the 804Ns and their bass capabilities are not much to write home about, and especially since you’re using a sub I think you’d be giving up more in sound quality than improving bass/dynamics.  If you feel like upgrading the center it certainly can’t hurt but not sure you’ll get a big improvement as the designs are quite similar.  What’s the rest of the equipment in your system, and is your priority more 2 channel or HT?  Depending on this you may be better off putting those $$$ to work elsewhere in your system so definitely take that into consideration. 

I'm using it 50/50 music and movies. Denon receiver and Denon 2 ch amp, that I want to replace for another 3 ch amp eventually.

The main reason for upgrading to the 804s would be if you wanted a fuller, more bass heavy sound and to do a better job filling the room.  I find bookshelves tend to struggle with large rooms at higher volumes then their floorstanding counterparts. If the sub is sufficient delivering bass, and the speakers/amp don't sound constrained at your listening volumes then I'd stick with what you have.