how is it that your 5 inch monitors can't keep up?
Do you listen to very loud volume?
3 or 4 inch should even be able to keep up with a 10 inch subwoofer.
Combining them gets you a full spectrum of tonal frequencies.
You need to dial in some things on the subwoofer like phase, cross over frequency, stuff like that. Also, some room treatment should be good and placement of the monitors and subwoofer. Room modes is something you need to keep in mind placing the sub.
Anyway, should be able to work together.
Unless you mean your 5 inch monitors are utter crap