Floorstanders vs Monitors and bass response

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?

Generally lowering the cross-over point of the sub is advantageous in a few different ways. Usually the only disadvantage of a floor-stander is that the cost of building a a larger box with the same integrity of a smaller box, and the added cost of shipping that larger box makes the cost of that larger box go up exponentially. Since you don't seem to be overloading the room with the sub, going with a high quality floor stander in place of a mini-monitor would usually be an improvement.

There are also good reasons to keep a higher x-over point, regardless of the main speakers' low end extension. First among these reasons is that properly placed subs (i.e. near the room boundaries) will (with very, very few exceptions) produce much smoother in-room bass response than main speakers (which are usually optimally placed away from room boundaries). In the rooms that I've measured, this will be usually true to up above 150hz, and has always been true to a minimum of 70hz to 80hz, regardless of passive room treatments, which have never been effective -IME- below this range.

One caveat: If you EQ your subs, the analysis changes a fair bit.

IME, you'll probably do better leaving the x-over point at 80hz than lowering it - and the bottom 2 octaves should sound pretty similar to what you're getting now. However, if your system allows, lowering the crossover point for a trial comparison test certainly can't hurt.

Marty

If you have a crossover as I understand it you are taking the base away from the main, hence the base will be the same other than it may change a little because you are changing the room. The mains are not receiving base so therefor changing the mains you are only changing the 80 hz or above sound.