mtnb1kr,
I had a buddy of mine that bought a used DC3 as well. Same kind of thing as you, mainly a bedroom player. He wanted it to sound like my Mark III combo but he, nor I, could get his DC3 as beefy as the Mark. I then let him borrow my Mesa Theile 1X12 cabinet with an EVM12L in it and it certainly had some beef then.
After thinking about it for a while though he decided that he didn't want to do the extension cab thing so he bought himself a used Mark IV wide body combo and sold the DC3. He has been happy ever since.
The DC is a great amp, but it is an EL84 amp. Some guys, and maybe this is you, just prefer the big tone of a 6L6 tube.
I would try and borrow a closed back ported front extension cab (like the Mesa Theile) and plug the combo speaker and the extension cabinet in at the same time. It should get rid of that nasally sound. Remember to use the 4 ohm outputs of the amp, there should be two of them.
I don't know if you have the manual, but it has some excellent starting points. Here is a link to the Mesa manuals page:
http://www.mesaboogie.com/manuals/user_manuals.htm
Check page 14 in the DC3 manual for sample settings. I think that sample 1 for clean and sample 4 for lead may be what you are looking for. Then just use the center slider of the Graphic EQ to tune it. Make sure the graphic selector on the back is on the in position, otherwise depending on what it is set at it may not be on.
chedgeco... 8)