QuestionHow can i improve the sound of my home theater sound. i am using a Marantz mm9000 preamp energy rear speakers and sub and Vienna center and front right and left. The system seem to me flat.
Answer"Improving the sound" of your system could mean a lot of different things...what is pleasing to you is a wholly subjective experience, so it's tough for me to give a definitive answer.
With that said, here are some things to consider:
You may want to make sure your speakers are arranged (height, angle) properly for your room.
Look into some acoustic room treatments (some examples can be found here:http://www.acoustimac.com/acoustic-panels/) This will help eliminate sound reflections that can cancel certain frequencies, which result in "bright" or "bassy" spots in the listening area (some could describe it a "flat" sounding as well). Here's more info: http://www.ndt-ed.org/EducationResources/HighSchool/Sound/interference.htm
Don't be afraid to utilize any equalization hat your preamp/receiver has available. A little "tuning" of your system to the space it's in can work wonders.
THINGS TO AVOID:
DO NOT try to "tune" your system by spending a lot on "audiophile" cabling. This is an incredibly slippery slope... there are MANY companies who would be perfectly happy to sell you a $1,000 per meter (or more) set of speaker cables that they bought from a Chinese distributor for $1 per meter, and then "dressed up". While quality interconnect & speaker cable is important, it isn't the end-all for your system, and it does not need to break the bank.
When tuning your system/room - be sure to listen to it at a decent volume level. At different volume levels, the human ear "hears" differently from a frequency perspective. This article can explain it a little better than I can: http://en.wikipedia.org/wiki/Fletcher–Munson_curves.
If you tune your room at a quiet volume level - where the "hearing curve" isn't very flat - you'll find it will sound VERY different when listening to something at volume.
I hope this helps you out a bit. If you have any more specific questions, feel free to hit me up.