In the years when I used a Marshall 100w Super Lead (two inputs, both clean and tied together), I tried to find a good distortion pedal solution. I tried Big Muffs, various Boss distortion pedals, a Korg G1 distortion processor (which I still have and don't use), and a Dynastar tube distortion. The Dynastar was the closest thing I found to the sound I was looking for. It was able to add the balls I wanted on my Marshall. Finding one would be next to impossible though. I think they were only made and sold in and near Fresno, CA (my hometown) about 10-15 years ago. I've only ever seen two.
The G1 also wasn't bad for what it was. It had 9 programmable presets. It also had an awesome octave-fuzz effect which I might actually use someday. It did sound a bit processed though.
I think it's possible to find an awesome distortion pedal solution for you, especially if you already like to overdrive your amp a bit.
Your best bet is probably to run down to your local Guitar center, bring your amp if possible, then just go nuts with all their processors and pedals till you find something you like.
Also, if you end up using a separate distortion pedal, I think it's supposed to go in the chain LAST. So you don't give a distorted or a really heavy signal to your other effects. Sometimes using one effect to pummel the input of another effect with noise can make some great sounds, but usually it just ends up noisy, especially if you are voilating the input of a digital effect.
