I don't know how you'd get out of that lease without spending big $$$.
You could put it on swapalease or leasetrader and see if anyone bites on it. Still, you'd take a financial hit doing so.
It'd probably be cheaper to buy the ///MSport parts and mod your existing X3. But, you'd have to put it back to stock when the lease is up.
Or, you could give your existing X3 to your wife/kid/parents and go get another. Once again... pricey option!
So.... I'd just try to enjoy what you have. I'm sure adding a subwoofer or amp might help pump up that audio a bit and satisfy you that way.
2013 X3 3.5 | SAP | DHP | NAV | CWP | AW | Mojave