To question #1, what does your system entail and from where are your connections coming? I need that info before I can answer.Using your own logic here, if I turn off my subs, I lose the low freq's. If I turn off the tops, I lose high and mid freq. Does this now meet your definition of a 3 way?
A 2 way with added bass? How does one 'add' bass? My top reproduces a range, my 12" reproduces another and the sub reproduces another - all within specified parameters. Your definition of a 3 way, (top, mid and bass) is exactly what I have. I do not have a top and mid/low with another low.
To question #2Added bass is just that, you plug in another Bass Cabinet(s).
The definition of a Three Way System is where you have Tweeters reproducing a high range of the musical spectrum, Midrange Speakers reproducing the middle part of a musical spectrum and Woofers reproducing the Bass/Lower range of a musical spectrum. There has to be two cut off points, one between the Mids and Highs and the other between the Bass and Mids. That can be achieved by the use of an Electronic Crossover or with Passive Filters. Newer amps may have an onboard DSP so if you set the cut off points in the amp providing the speakers are capable of reproducing that tailored signal.
The best use of a 3 way system is to have it tri amped. The transducers will then receive an amplified dedicated signal.