I ran a 4.2 setup without a center channel for a long time. Unlike the abundance of 2 channel 'purists' out here, I did not hesitate to upmix 2 channel sources to DTS NEO 6 music and multi-ch stereo if i felt like it. I don't feel like arguing this with the 2 channel purists here either. Watch this video/discussion with Gene and Matt (There are some bits of information you may appreciate, especially the part that goes into why 2 speakers are not enough and what you miss with 2 speakers).
Eitherway, as my collection of native 5.1 SACD and Blu-ray audio mixes grew, i decided to get a center channel. Many center channel speakers out there are flawed by design. So, get one that's least disruptive by design and set it on a dedicated stand with breathing room (not shoved up some entertainment cabinet, etc). Treat it as you would a front main especially IF MUSIC is your priority.