You do not want a sub on the center channel. Male voices will be sent to the sub, and it will smear, distort, be hard to understand. Usually you cross the center over 100hz. The HT receiver will divert all bass to the subs, no need to add an extra one if you are using LFE. That is why it's there in the first place.
Any HT/multi ch recording will have 80% of the sound going to the center channel. Unless you have your HT setup perfectly music will sound like it's all coming from the center. Truth is you have your center setup incorrectly. It should play at the same volume/db as the rest of the speakers.