What is wrong with a sub?

I'm too new and inexperienced to take a side.  But as I posted - I like tube amps.  I like how they sound.  As such at reasonable price range tube amps there are no ribbon speakers I can use.  The subs having their own amps move the air fine.  I also like the argument that the position of the subs may not be where the mids are.  

Good subs add an "atmospheric" thing to a hifi system that has to do with charging the room with frequencies that exist in real music played live, not necessarily chest thumping low notes although they can do that also of course. My my main speakers have a very accurate low frequency range that sounds excellent without subs, but dial in the subs and man...something is just there that ain't otherwise...orchestral music sounds like it's in a real acoustic space, pianos sound like hey, that sounds like a piano! Subs aren't and never have been "lacking respect" in the audio community so don't get hung up on low notes, simply enjoy something closer to what music is supposed to sound like.

first 2 subs are a lot better. I have 2 and have experimented running just one. No comparison  The Achilles Heel  is when come with a built in plate amp with volume control and cross over point. Most of these are crude and cheap

Emerald Physics make a interfacing product called The BOM (bass management) which works pretty well for ~ $300, but to get the best Marchand offers excellent outboard active XOs, but they are costly

David, I am hesitant to use different makes and models of subs when putting multiple in the same room. I’m not saying it can’t be done or that it can’t sound great but I believe you stand a better chance at integrating them when they’re all the same model. If you already have multiple subs and want to try it out, let me know what your results are. 

As for DSP, it stands for “digital signal processing.” Some subs have it built in. With my system I added a MiniDSP inline with the signal going to the sub amp. It lets you tweak the signal in virtually unlimited ways based on what programs you upload to the DSP. I use it to cut and boost problem frequencies which are caused by my room modes. You can also adjust the phase, time alignment, delay, add filters, high pass, low pass, etc.