Hi, thanks for your reply...in order to learns to edit surround, i need to monitor it as it is hard to learn if I dont hear it.
I assume that I need an external audio card with analog out and also a received with analog in...that is what i read on the internet but nothing specific I have found.
We did recently set up 5.1 monitoring in our suite. You can choose an interface with both in and out, preferably with balanced XLR or 1/4" outputs. I know we did get a little buzzing until we switched to balanced cables. Specifically, we're using a Focusrite Scarlett 18i20 which actually has a ton more outputs than needed, but it fits on a rack and does a lot for the price. You can also try something like the Steinberg UR28M which is a little cheaper and has enough outputs. There are a wide variety of more expensive interfaces as well.
The Focusrite Scarlett has a program that configures its in/out routing, and all you have to do is set outputs 1-6 to line out and plug in your speakers. We generally set output 1 and 2 to be monitor 1-2, so they can be controlled together. In the system sound settings, you set it to output to your interface, and FCPX should be aware of it. One other program you may be using is Audio Midi Setup, but I don't think you'll need to be changing the defaults here.
One important thing for 5.1 monitoring is using an audio meter and setting the levels of your speakers properly. There are apps for smartphones that do this well, or you can get a dedicated audio meter. You can find some videos on Youtube that show you how to do this. It's also important to have a matching set of speakers.
I use a Black Magic design Ultra Studio Mini Thunderbolt to HDMI. I lead the HDMI signal thru a 5.2 channel Sony Surround amplifier and on to a HDMI monitor. This is a low cost monitoring system. But it works. Put the FCPX into 5.1.
Change any sound source to surround in inspector .
For that particular Scarlett, yes, the outputs are all in the back of the unit except for the headphone jacks, and the speakers should be connected to those outputs (not inputs). And the configuration is pretty straightforward because you want each speaker to have a direct signal. I have 1-2 as Left and Right, 3 as Center, 4 as LFE, and 5-6 are Rear Left and Rear Right.