Are you doing true 5.1 audio mixes or are you upmixing 2-channel mixes?
I absolutely never use center spread, and when dealing with 5.1 mixes would expect it to be deleterious to the intention of the mix. I'm not saying it's wrong, especially if you enjoy it, but matrixing one discreet channel across three would change the intended effect, especially if the engineer is worth their salt.
Are you finding this to be the case with the Horizon in place instead of the S2? Considering that your new center should be as capable as your towers, I would expect you should be able to do away with the extra processing and get the right effect.
I could carry on about my feelings about upmixing stereo, but will spare you.
I know several people here have been doing so and enjoy it. Again, not being one for dogmatic bs, if it is enjoyable then do what you want!