Thats a good point. To explain a little on the dshowhelper.dll thing, there's a well known technique called 'clutching at straws', I felt that on this occasion this was the most appropriate course of action .Remember the tv works fine with the old tvcapture.dll
The log shows the information that I was expecting from a working box (i.e. same results as I get) so that one can go in the bin too and at this point I'm going to have to bow out of this one, the approach I was taking was to make sure that there wasn't a COM error occuring due to different versions of the filter and similar issues - which is more or less how the problem is reporting itself to MP.
It'll be back to dman now, his DirectShow knowledge is better than mine. Failing that I think we're going to have to wait for Frodo to return as its in an area of the code that has received a lot of his attention recently and something that we could very easily mess up in a big way and/or could end up going around in circles .