It all depends on what bars you get. I have an OEM Integra Type-R rear swaybar on my EJ6 Civic, and never had any conflicts with the rear lower tiebar I used to have, before I upgraded my rear LCAs for some lighter weight Megan Racing rear LCAs. But some bars will have problems while others won't, simpley due to design and how they mount to the suspension. The ITR bar is nice because it's exactly like the OEM Si rear bar, only it's 22mm instead of 13mm.
H-braces are GOOD. I just put one on my Civic last week. Of course i had to adjust the dampening on my Teins to adjust for the additional understeer that the brace created, but my steering feels a little more precise, defined and quicker. Can't seem to get the rear of the car to slide out as much as it used to, which is fine with me.
For my bars/brace setup I have as follows...
Front: Neuspeed upper front strut bar
Megan Racing H-brace
Rear: Intergra Type-R 22mm swaybar w/
Beak's kit
and very soon to add Cusco solid one piece rear lower tiebar to replace my old Arospeed hinged type generic style tie bar.
The rest of my setup includes my Megan Racing rear LCA's and my Tein SS coilovers with +2kg spring upgrades at all corners (10kg front and 6kg rear)