Digital BW, The Print

>I'm thinking of making up a poor man's monotone septone set 
>for a 2200 out of the quadtone MIS full spectrum inks.

Note that the UT-R2 inkset is another possible source of inks.  The R2
"neutral" (cool) has a less cyan tone than the UT-FSN, particularly the dark
gray C position.  While the dark grays are the same density, the light R2
midtones are darker than the FS M position inks.  They were designed for the
Epson driver cross-overs.
 
> Is anyone familiar with how dark the light grey of a 
> quadtone set is compared with the
> lightest tone of a K7 set...

No, I've never worked with the K7 inkset. 

A draw-down test setup is the easiest way to judge relative densities.  See
http://www.paulroark.com/BW-Info/Draw-Down-Procedure.pdf 

>should I be thinking of getting 3
>additional tones by simply mixing eboni 

Eboni is not in the same ink family as the PK, LK, and other UT and MIS Pro
color inks.  It does not mix well with them.  Use one of the PK or LK inks
for grays and the color inks as needed.  The midtone UT inks are all
compatible.

>with DG; DG with MG; and MG with LG...or would getting the 
> lightest tone from mixing LG with base be a better approach.

(I'm not familiar with your abbreviations.)

>Re mixing... I was thinking of pouring two 4oz bottles into a 
> virgin pint bottle, ...

I use a digital gram scale for precise mixing. 

You don't mention what driver or rip you'll be using.

Unless you are experienced with these matters, I'd recommend you use a
pre-mixed inkset.  You may be getting into something that will turn out to
more complex than you'd anticipated.  

I've tended to move to inksets composed of standardized densities, in part
to get away from the inconsistencies that can crop up in mixed inksets.
Although even the standardized inks vary, at least I've eliminated some
sources of errors and inconsistencies.  

I might add that my original variable tone inkset was made in part because
it appeared that controlling tones via software was easier than doing so via
mixing.  All I really wanted was a "neutral" inkset, but mixing an inkset
that was "neutral" for more than one paper at one density was more difficult
than I thought it would be.  Back then I had no choice but to use at least
one toner, and after than the number and complexity of toners started to
multiply, particularly as I tried to get better control of the tones.  With
today's good printers, however, much less is needed.  In general, I'd say
the less mixing you need to do, the better.

Good luck with your project.

Paul
www.PaulRoark.com