Single driver vs traditional 3 way loudspeakers

Interesting
I recall a  ONKYO amp I had back in the 80's had a  built in  5 level EQ.
I liked playing with it.
I just ran all EQ's all the way up except the middle eq.

I'm not that interested in the EQ test, although as you say might show some weakness.
You might find usage as you design and build for customers.
I'm pretty happy with the 2 DL's, and am sure the additon of  the Tang band W3 will also add some nice charms. 
I knid of ... you know what,,,In fact what you are saying has some truth...The DLVX8 all by iteslf is quite livable, I have no issues with it as a stand alone speaker
But thought, since I have the DLW4 just sitting in the closet,,why not see what happens along with the DLVX8. BINGO,,the EQ's missing in the DLVX8 were padded by the EQ's in the DLW4. Diana Kralls voice just came to life. 
Apparently whatever EQ's were weak in the DLVX8 were padded by the EQ's in the W4. 
No speaker is perfect flat response.

EQ just for test, must me 10-12 grade at least, i used digital , build in some program so you have to be able boost 200-300 Hz. i am sure you will be surprise, actually it does not matter for customer or for yourself, try and let us know

Not sure where to get this EQ you are talking about.. Ebay??
Price?
The WBer experiements set me back, audio budget very tight.
So what is your purpose of testing EQ in your lab. 
To ck to see where a  speaker is weak?
I am not sure what the reason is testing EQ?
I am sure if I hook the W8 or W4 or even my complete 4 way speaker to some EQ gadget, like having say 10 EQ levers,, I am sure the sound,,or lets say, some fq ranges that I perfer might geta boost in some recordings. 
But then the  musc has to pass through this gadget = more distortion. 
EQ gadget may boost FQ's, but adds distortion. 
The EQ thing on the Onkyo sounded better in off mode. 

Not sure why you don't play around with the davidLouis VX6 and add in a  TB W3. 
Then add   a pair of DavidLouis Magnesium 8's per cabinet and then add in the Davidlouis Be/Nd tweeter.
25cm , not the 28.

I think you''ll be pleasantly surprised. 
That combo will beat my system, perhaps, ,,
magnet system is a  beast.
IMHO Magnesium is the best cone material to intergrate intoa  WBer system, as its neutral /not warm.  vs paper types which i don't like. 
I know you offer paper 10's, not my cup of tea. Too muddy/boomy. 

https://www.ebay.com/itm/324521174123?hash=item4b8ef8246b:g:BFIAAOSwoRRg1EKi

Price ?  Free, Online downloaded, sorry  i did not remember, which one

You are quite right Eric.
Tannoy makes coaxial speakers.
Coaxial speakers provide the magic that those with full range drivers are looking for.
Maybe that should be rephrased. What I assume those with full range drivers are looking for.
Tannoy and Altec got it right decades ago.
Point source is where it's at.