Guidance for speaker upgrade

Might want to add a high quality subwoofer. I own a Rel Storm 3, augmenting Intuitive Design Summits. Those already go so low that the crossover on the Rel is set at 27 hertz.

There's no reason at all that a floorstander couldn't be used with a subwoofer IF the subwoofer is well integrated and IF the subwoofer is restricted to reproducing the lowest frequencies (by setting the crossover low enough). In my opinion only the very largest floorstanders are truly "full range." For example, my Paradigm Studio 100 V3's benefitted tremendously from the Rel Storm 3 I was using. However, the crossover point was set at something like 28 hertz. With my current speakers, it's set even lower at 27 hertz. One caveat is that the sub has to be up to the task.

Pjboud,
Do you have a ballpark figure for your speaker budget (including any subwoofer)?

If you're truly satisfied with everything about the sound of your system except for the bass, then I'd strongly consider keeping the speakers and spending as much as necessary (up to the budget level, of course) on a truly high end subwoofer, but the selection process may take some time. Proper integration is absolutely vital.