I understand - I was here a long time ago too.
Not trying to irk the purists.
But logically, when you expect a 5/6 inch driver rated at maybe ~50hz to reproduce decent bass, well...
In my humble experience most speakers up-to a certain budget (or MAYBE any budget) with that kind of driver size can't reproduce enough bass below 80hz, some do good around 60hz, but that is rare. There is a fair amount of information in "most music" upto 40Hz odd as the low E string of a standard tuned bass guitar is around 41HZ. Lowest notes on a piano can be around 25-30Hz (maybe lower). Hard for most bookshelves to do.
Please note - I said "good sub". That is important
More important is integration. I have never had great luck with a full range sub setup like RILs. However subs with LPF/Crossover around 80-100Hz, have been brilliant in my case. When you take the low bass duties away from the speakers with 5/6 inch mid bass drivers,
I feel they do much better.
I also feel,
a subwoofer is as important in a stereo setup as it is in movie watching experience, but I gave up ages ago trying to be a purist.
I am not trying to convince you to not go for a speaker upgrade (I am no one to suggest anything like this - I buy new audio gear every month) - but as you said you like the sound of your speakers - hence. A new toy is always fun. Best of luck with your search.