can u use a eq with a 5.1 system?

Answer 1

I assume you mean a separate external equalizer. In order to do that you have to have access to the individual channels between the decoder/preamp and the main amp. Many higher-level A/V receivers have "preamp out" and "main amp in" connectors that allow you to intercept the signals. If your receiver has that, you can use an external equalizer. If not, there is no way to do it. Check the manual for your receiver, it should give instructions on how to include external components between pre-amp and amp. Lower-cost receivers do not have this feature. You will need an equalizer for each channel you want to control. If you are only interested in balancing the main speakers, a stereo equalizer will work. If you want to also balance the surround speakers, you will need another stereo equalizer for them.

Many A/V receivers have built-in equalizers for each channel. Again it depends on the receiver (mainly its cost).