The only way I believe to keep your stock grill cover on the tweets are to make sure you find a very shallow tweeter, as well as one with a flat front, as most come with a dome shape. You don't have very much room at all back there, even when taking the grill out...so good luck.
I didn't have Monsoon, but I assume that it doesn't cost much to get an amp and a sub to fit, you have plenty of room on the other side behind the driver seat to throw an amp in. If you're keeping the stock head unit, the sub will still work, if not...she won't...so think about that.
I rewired my entire car with better sprk wire, and it was a pain getting to the front doors, but well worth the effort....if you need anything else, forum members are a really good source