In my case, I bought a router a few months before I even got internet; planning ahead, so to speak. I knew that if I got the internet first they'd either ding me for renting some crappy wireless-G router every month, or I'd have to get one anyway. So I got a rather nice Draft-N (wireless-N was draft at the time...) router, which also had gigabit LAN. I actually ran it wired only (though others in the house used the wifi and I didn't get any complaints) for about a year, until I got the laptop I'm typing on now, which I selected to have built-in wireless-N capability. The speed was really something; particularly network transfers between machines, which could use the full speed of the router. The internet itself was I believe 50mbps download and 10 mbps up.
PS; Not sure too, what a more powerful antennae would do to my sound system. The router as it stands sends a constant clunking noise to my speakers. Enough that I'm still attempting to find proper placement.
You haven't really described the sound system... I guess it's wireless? If so you could probably change it to use a different frequency.
I have interference problems, too; first, my wireless card that was in my PC would sometimes interfere with the audio card circuitry. I was able to mitigate it somewhat by rearranging the connections, but I only have a few PCI slots and both cards are PCI so I couldn't move them very far apart. More recently the wireless-N card seems to have died, and I removed it from that PC. The sound issues were far less, but they still exist. I was however able to actually trace it to the speaker system itself, which is just a 2.1 system with two speakers and a subwoofer. It has an external volume control, and moving this around would change the intensity of the interference, and covering it with a CD, tin foil, or other electrically reflective material would deaden it too.
The applicability to your situation- first, you have to try to find where the interference is occuring (assuming changing frequencies doesn't resolve your issue). In my case that "weak point" is the weakly shielded volume control. Then you simply have to "shield" it somehow. in my case I was able to just move that control a bit.
On the other hand, in my case I wasn't picking up interference from a nearby wireless router since it hasn't been connected in some time. I was picking up interference from other stuff, like wireless routers, USB hubs, the electric motor on a desk fan, my monitor, and my USB TV Tuner. The biggest interferer I found was with a HTC smartphone I used for tethered net access a few times, which was so loud I had to shut off the speakers for the duration. (Sticking a CD or other metallic "shield" between it and the volume control and all was silent again).