Hi, Joshua:
Notation Software products do not currently support any type of audio plug-ins.
It is possible to create a work-around, using a virtual midi port (such as Maple Midi or Hubi's Loopback) and a stand-alone host for the plug-in(s).
I use Herman Seib's excellent freeware VSTHost and SaviHost programs for VST's and VSTi's.
The only stand-alone DXi host that I can find is Console by ArtTeknica. You can find a demo here:
http://www.hitsquad.com/smm/programs/ConsoleSMS/
It is not, unfortunately, freeware, but I can't seem to find a freeware DXi host.
I'm not sure whether it is because DXi are harder to program than VSTi or what, but it seems that the DX plug-in industry is much more focussed on commercial/retail release than freeware.
However, most DX plug-ins have sibling VST versions or, certainly, equivalent ones. You might consider coming over to the dark side.
Good luck.
David