Changing speakers naturally implies that the bass will be different. The full range speakers may go lower as indicated above, you may need to lower the Xover freq point.
Do you own an acoustical measurement device so as to take before and after measurements to compare the current Vs intended future speakers? You will also want to use the measurement tool to optimize the bass by trying different speaker, sub, and listening chair locations.
I have been using full range speakers for years before adding a pair of subs (Rythmik F15) last year. Here is my experience.
* use the measurement tool to optimize the mid and high frequencies, imaging, tonal balance etc. Of the main speakers.
* use your sub location to augment the main speakers' bass response. Have you considered using two subs to get even better bass across more than 1 seat and also to improve the bass at the primary listening chair?
* measure the Freq Response Vs SPL below say 500Hz for all possible sub locations with the main speakers playing too so as to see the constructive and destructive bass freq interferences.
* In analyzing the various measurements of all the candidate sub(s) locations, you may want to be mindful of the "Equal Loudness Curves" that has the bass frequency SPL rising as freq falls to accommodate the decreasing sensitivity of our ears at lower frequencies.
* Measure your mains and one sub playing. Then turn on your second sub and experiment with the second sub's Xover freq, phase and volume such that it's additive effect has the desired impact on the bass freq response. In my case I have 20Hz being about 12~15 dB higher than 300Hz.
* most people place their subs on the floor which helps deal with the length and width bass modes. However, there is also the vertical dimension to contend with. I raised one of my subs above the mid-level of the room's height, and low and behold, a bass null was removed which was due to the vertical dimension.
* are you using bass traps and parametric EQ as other tools to optimize your in-room bass freq response and bass decay times?