now that you have removed the stock filter, my suggestion would be to use an Astronomik CLS-CCD clip-in filter, and then if you're desperate to mod further, to look at a cold finger mod. Both of these options will help to improve signal-to-noise, which is what these mods (and the progression to cooled mono high QE) help to achieve.
I ran two cold-finger modded canons for a while (albeit from dark skies), see
here for some deep-sky examples (note the lunar pics in that link were taken with another camera). Dark noise is reduced considerably with the cold finger mod