Can Late 2012 Mac Mini support two QHD Monitors?
Am I right to read this that my Mac will support two QHD monitors but
only by splitting from the DP/thunderbolt port leaving HDMI-out
unused? In which case can I get a Thunderbolt-&gt;dual DP or DP-&gt;Dual DP
adapter or do I have to get a DVI splitter and two DVI-&gt;DP adapters?!

There's no such thing as a Thunderbolt &quot;splitter.&quot;
You are confusing the term dual-link DVI with dual DVI.  Dual-link DVI refers to the number of data channels (double) that is available for more bandwidth meaning higher resolution.  It's not a &quot;second connection&quot; and you cannot &quot;split&quot; the signals.  Dual DVI is two DVI ports for multiple monitors.  The Mac mini does not nor support dual DVI
Multiple Monitors on a Mac mini
The Mac mini will natively support two monitors:

Thunderbolt/DisplayPort - Quad HD (2560x1600)
HDMI Port - Full HD (1080p)

To get another display or dual QHD displays, you need an additional adapter and for the Mac mini, that means USB:

USB 3.0 to DisplayPort -  Ultra HD
USB 3.0 to HDMI  - Ultra HD

This will give you another USB adapter, but be aware that you are now offloading all of the graphics processing onto the USB bus and ultimately on the CPU.  In other words, this is not something for performance, but rather convenience.  The Mac mini wasn't designed for this type of setup.