Here are some of my thoughts that might give you some idea which route to take.
This should keep you thinking until one of the real "Gurus" come along.
The answer is not quite as clear cut as you might think. The problem comes from the fact that you want to use sky plus with the projector. The other consideration is budget. The quadscan is very much at the entry level for scalers so I am assuming that you will not be using a £3000 stand alone DVD player.
However I would suggest :-
1) HTPC
2) Limo Pro
3) Quadscan
To justify the HTPC at the top you have to consider several options a £50 capture card ain't going to cut it. The best analogue capture card around at the moment is the Falcon. However I am not convinced it could beat the Limo Pro for Sky playback (although with the latest Dscaler filters its getting pretty close). To do the best job at the moment you need an SDI capture card and you need to have your sky plus unit modified. (Jeff's your man here!). In this configuration I am sure you would get the best of both worlds.
A few words on HTPCs :-
There is more to an HTPC than buying the right bits, screw it together, switch it on and hey presto. My HTPC has been developed over a period of a year and has gone from OK to fairly exceptional in that time. Most of my developments have been in software rather throwing expensive hardware at it. An HTPC can be a tweakers delight but once you get everything the way you want it it can be controlled by a remote control in a similar way to any of your other home theatre products. A poorly concieved HTPC would be at the bottom of the list but a "proper" one should happily live at the top.
Why HTPC ?
In a word flexibility an HTPC can handle multiple screen resolutions, multiple refresh rates, 2:2 Pull down for PAL, 3:2 Pull down for NTSC, multiple screen ratios and more all in its stride.
The good news
As time is currently on your side over the next year major advances are coming with regard to capture cards and by the time you are ready to buy you will have several other options available.
As ever it is really up to yourself what you are willing to consider. For some people The HTPC is a non starter because they want a "Plug and Play" solution. However as far as bang per buck goes you will find a well configured HTPC hard to beat.