Yeah, Digital SD is very poor on Videotron, always has been. I watch mostly HD, so I can live with it.
If you want a better SD signal, StarChoice or ExpressVu are better options (I personally prefer StarChoice). It looks like the DSR530 has been finally fixed, so they're an option now. Bell is offering free PVR rentals for new 2 year contracts too.
One tip for Videotron tho: If your SD program is being shown on the HD channel, it offers a much improved picture. Try that out first.