Help with display management

[Kevin O'Gorman]

I'm running xubuntu 14.04 LTS, and have just replaced my mobo and graphics
card with a new ASUS Z97 deluxe with onboard graphics.  The old card was
nVidia, the mobo uses Intel graphics.

When I restarted the machine after the mobo-ectomy, xubuntu would only
recognize 2 of my 3 monitors.  The mobo advertises it can support 3 with
resolutions up 'way beyond my actual HD monitors.  I created some space,
and installed a fresh copy of xubuntu 14.-4.2.  It works fine.  I've
removed all nVidia things from the old system, but it's still broken.

In both installs, both new and old, I can try to manage the monitors with
the whisker menu's action item (at the bottom) for "All settings", with a
gadget called "Display".  I don'[t know the proper names of the packages
that provide these things, but I hope it's clear.

So I either have to replicate my other configurations in the new install,
or somehow figure out what's broken in the old one.  I'd prefer the latter,
if possible.

Details of what's wrong:
The Display gadget shows 3 monitors, HDMI1, HDMI2 and ACI23" -- and these
are arranged physically left to right on my tabletop.  They are all three
the same model of monitor.  Normally, I have HDMI1 and HDMI2 working.  If I
try to mark the 3rd monitor's "Use this output" then one of the first two
will go dark.  I cannot get it to use all three at once.

I don't know why they're called what they are since all three moniotors are
identical.  What's oddest is that the one that's marked ACI23" is the only
one that is actually HDMI at the computer end.  The others are a DP and
mini-DP connector.

This is a configuration problem and not a hardware problem.  I know this
because the fresh install of 14.04 does not have this limitation, and works
fine with all three monitors.

So what do I do to get the three monitors?  Probably just ditch a config
file somewhere, but which one?

-- 
Kevin O'Gorman
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