Aftermarket set-top box? Any better?

[skap7309]

Hi there,
A simple question here; would upgrading my Sky box improve picture quality or is it purely down to signal strength? Sky only seem to supply Amstrad or the likes of Grundig as standard and i have been less than impressed over 'pure' analogue pictures.
If this is the case, any suggestions on a favourable model/price?
Thanks, look forward to any replys.

[MartinImber]

How about something like the Sony VTX800U?