Hi and
The signal from a Virgin (or Sky) set top box is not compatible with DVB-T cards, Freeview is only available using a suitable aerial.
I'm not sure about the DVI socket on the monitor being compatible with being fed directly from the HDMI port on a V+ box, but the RF socket is definitely disabled if you use HDMI, the V+ box has no passthrough, or combiner, afaik.
I guess it is a case of which channels you want, if you are happy with the Freeview selection your best bet may be the aerial upgrade, unless someone can confirm your monitor will be ok fed directly from a V+ box??
DRM 'shouldn't' be a problem, provided your monitor is compliant.