The two buss (also called 2bus, stereo bus, and mix bus) is the final buss you mix down to. (I had to look this up not long ago as it was confusing me). From what I've read around here, I started putting Waves SSL bus comp right on my 2bus before I start mixing. It only hits the signal by about 2db, but it is enough to "glue" it together and as mentioned earlier affects the stereo field. It's VERY subtle, and I use the Waves SSL because it seems very transparent and open to. (side note, I prefer the IK SSL comp better for drums as it is a tad more aggressive). I used to mix up stream, so I wouldn't have added that compression until the end. Now I find it nice to mix into it. FWIW, I also mix into Slate VCC and Slate VMT...
I hope this helps,