Is your splitter HDMI 1.3 spec I wonder,and HDCP compliant?
By deduction,as you are only experiencing problems since installing the new pvr,the problem is there.
The new Virgin pvr is quite something,and may have all sorts of interacting nonsense present on it's output.Sky hd pvr's for instance,won't output if they can't establish that the next device is HDCP compliant
For what a current 1.3 compatible splitter will cost,it could be worth trying one?
Nick