Digital BW, The Print

>  However, I am experiencing frequent clogging of my heads requiring
> head cleaning often. I'm not sure why this is occuring or what the
> 'cure' is. 
You did not give very precise info about the type of carts etc. So the
following is general advice based mostly on personal experience.

I used 1290/1270 printers for a few years.  Eboni worked very well in
two (one I used for for colour on matt paper -CIS, and one I use for
FS-N or matt/gloss paper swapping the black - refills). I had the
following problems 

random, occassional "clogging" (almost always air), mostly on the T009
cart side, rarely on the T007 side -  retrospectively I suspect
poorly-fitting carts were admitting air where the cart meets the printhead

increasing problems with foam in CIS and refill carts with sponges,
after ~1 year (CIS) or about 10 refills it was necessary to change the
carts.   It would be easy to make foam and get problems if you filled
the eboni cart too fast - if there is much foam suspect that and try a
new cart.  Eboni seems to foam more than most inks (that I've tried).

after changing to spongeless carts (MIS original version) I had
several "catestrophic" leaks where all the ink from the cart would
flow out over a day or three.  This was due to a combination of design
and manufacturing quality of the carts.  Apart from this problem
(mostly with T009, but once or twice with a T007) the spongless carts
were better from a clogging point of view.

I have also read about (but NOT experienced) a problem concerning
mixing of dye and eboni ink on the parking pad.  Older 1280s etc. tend
to have quite a lot of ink around the pad and parts of the underside
of the printhead.  If you introduce eboni there is a chance that they
mix, and the mixture becomes very viscous causing problems.  
You could search for more on that, cleaning it, etc.  

One problem with clogs is they can be due to air or blockages.  It can
be difficult to tell these apart, but varying nozzle check patterns
are suggestive of air problems (blockages should stay in the same
nozzles until they clear). 

I hope you know to do clean cycles in sets of 3, never more at a time
before making a (small) print.  If you have problems that persist,
especially just after refilling a sponge cart, wait a few hours before
trying again.  (I agree this is very inconvenient!)

I printed many hundred prints with these printers, with pigment inks,
and had only slightly more frequent problems than with my canon S9000
with dyes.  

Both 12x0 printers were replaced when they failed (I got them used,
and replaced them with used printers - one of which still works). I
have moved on to using a single printer that can take PK/MK
simultaneously.

>  In printing a portrait, there is a thin white line appearing
> horizontally about 3/8 inch from the top and bottom of the print. It
> is always in the same place and it does NOT appear when I make the
> very same print on my 1800.

If you mean across the print as you look front on to the printer, it
sounds like either an error in the dithering - where it transitions
from the pattern used near the paper edges to the one used in the
middle of the sheet (software)- , or some kind of paper feed error,
happening at the same transition (where the steps that the paper takes
vary, you could see that if you watch carefully with the lid open).  
(Guesswork!)

>   It has been frustrating and I am tempted to return to my 1800 for
> B&W prints since I had no clogging issues at all with the Epson inks.
> (Though I must admit I prefer the 'look' and feel of the 1280 B&W
prints.)

There is a chance that printhead variation means that some 1280s are
just not going to work with certain non-standard inks.  I've seen
evidence of this variation, and the many reports of frustrating
problems suggest some of them are just a dead loss for this purpose.  

Good luck! 
Ken