Yeah, they are starting to push really low at the bass fringes.
The Bagend cabs are OK, but will will get no volume from one. In a studio setting you might be able to get away with one, I would want at least two. For live performances 8 would do for a small gig.
The Whappo Grande, and 16H aren't that big a deal either. The WG is good for F#0. It is just a 21" driver in an enclosure with an F3 ~20Hz. The 16H is a RLH with a low corner ~30-35Hz. You would still really want two here live, if you really do much low low bass.
Ricci is right about the sealed driver having a hard time going that low and high at the same time. If you will look the WG is only rated for up to 400Hz.
Instrument subs are not like the loudspeaker most of these guys build, so you are not going to get a lot of good help here. Learn WinISD Pro, and just start throwing 21" drivers into a sealed enclosure you can live with. Look at 18Sound, B&C, Beyma, the usuals, and the the Peavy one as well. Pick the one with the flattest curve down to ~20Hz. If the Le is ~2 or lower you could do alright with just the 21". If it is over 3 you will need another driver. Just build another small cab to place on top of the 21" using a cheap 12" guitar driver. All you will need is to add a capacitor to it, set to ~300Hz, and an inductor to the 21" to work around the same Hz. Hook your pre-amp up to a two channel amp, attach each cab to a different channel, and dial in the highs with the amps attenuators.