Looking for a larger driver to fit with my 4" faital pro

Hi guys
I did purchased 2 pairs of 4" faital pro 4FE35 (8Ω) drivers (See below files with specs). 30W, 92dB, Fs100,Qts 0.85
I am using one of them in a sealed enclosure of 8.6 liters.
The drivers are very good especialy in mid high frequancies but I still considered more low frequencies are needed (lets say bellow 150Hz).
So I was thinking adding a bass or a mid bass driver and making a system with the one pair even something more powerfull using the two 4" Faital pairs.
What do you think and which large driver would fit here??
thank you
 

Attachments

Thank you
This one is 12 " sub woofer very powerfull it has a high Mms.
Is it suitable for HiFi use
What do you think about :
8RS200 8" with 93dB, Fs 50Hz, Qts 0.32 Xmax 6.92, Vas 16l, Mms 30gr, its a mid-low we can cross it higher freqiancy: FaitalPRO | LF Loudspeakers | 8RS250
10FE200 10" 96dB, Fs 55Hz, Qts 0.70, Xmax 4.67, Vas 54l, Mms 25gr, also mid-low FaitalPRO | LF Loudspeakers | 10FE200
6FE100 6" 91dB, Fs 61Hz, Qts 0.54, Xmax 5.25, Vas 15l, Mms 14gr Mid-low FaitalPRO | LF Loudspeakers | 6FE100
We can see other brands too.

I need you help.

I dont know if it would be better to use a low woofer to cross it at 200Hz or a mid low and cross much higher?