Kenzo,
Grinner's right about foley work. However, you guys look more like you need help with basic sound design. After I watched your clip, I listened to it a couple more times. Though it's just a test, you need more than just the punching sounds. Your clip sounds 'thin' because as Grinner mentioned you don't have 'layered sound' accompanying your live action.
Sounds that are missing: basic room tone, every interior and exterior space has specific and unique audio frequencies associated with them. Always prior to shooting a scene tell everyone on-set to shut up and be still then record about 10 to 30 seconds of the 'silent' room. You'll be surprised what you hear. You'll use room tone as your baseline audio track and lay all other sounds over it.
Next, you need the sounds of footsteps and foot movements associated with the action on camera. Remember, wet or dry sneakers don't make the same sound on concrete that leather shoes do. Clothing moving and the sounds of active bodies impacting the surfaces present onscreen. You can get most of this stuff in the field or on set by booming specific areas (feet, legs kicking, etc.) with a shotgun mic. Make sure there's no dialog going over it so you can single out specific sounds easily.
Lastly, when you don't have an area to be used as a foley stage, 'canned' sound effects are the next best thing. There are tons of great SFX libraries out there that won't put you in the poorhouse. Do yourself a favor and make sure they're Royalty-free. Unless your a prominent production house with serious and regular clientele, it's not worth getting contracted sfx. Sony's got a great 5-10 disc library that's affordable and works great with Vegas, Premiere and Avid products (I don't use FCP, it should work with it too.) Even with canned sfx, you still will have to layer your sounds to make convincing punching impacts and so on to make them convincing.
So when you're putting together your audio tracks even if you're going to lay a heavy music track over the action, you'll still need to set up layered sounds like I just mentioned. It's a bit more work, but unconvincing sfx will kill a flick faster than Joel Schumacher. I look forward to seeing and hearing the updated clip.
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