how do you trear rooms to bring up the null points

Any treatments applied near boundaries to reduce peaks due to room modes will also raise nulls because they are both fed from the same energy source. There are tuned absorbers which you can read about at
www.realtraps.com
http://www.quietconcepts.com/products-atp.htm
http://www.rpginc.com/residential/cinemusic-products.htm

OTOH, they are rarely needed as broad-band bass traps placed at boundaries (in the pressure zone) are cheaper and can be effective.

It is hard to treat the listening position(!) but you might be able to relocate it.

Kal

Nulls will generally occur in specific room areas. As Kal mentioned; you might want to try moving your listening position closer to, or further from your speakers. Often, it only takes a very few inches to make a difference.

OTOH, they are rarely needed as broad-band bass traps placed at boundaries (in the pressure zone) are cheaper and can be effective.

I agree completely - broadband traps is the best way to go unless you are an acoustic expert. The nice thing about broadband traps is that they cannot do much harm - in most cases they are beneficial - whereas a tuned trap can cause problems if it is not tuned and placed properly.

thanks for the tips. I guess it works like putting together the rest of the system - trial and error.

Well, there are alternatives:
1)Learn to use measurement and analysis tools.
2)Hire someone who can do it for you.

Kal

It's always easier to remove than add, even in the digital domaine. That being said try reducing any peaks with room treatments. That should smooth things out. Also, as has been said, play with speaker positioning and seat positioning. Small changes can have big effects.