Besides that mythical max tow capacity number, your vehicle also has a rating for what it can carry. The two ratings are greatly affected by each other.
IE:
If you tow a trailer that is at your max tow capacity, you have no room for any passengers or cargo. And, if you fill up the vehicle with people and cargo, you may not have room for any trailer weight.
Here's a link to owners manual for 04 SRX. See the section on towing. Particularly, page 4-51.
Once you know how much room you have for tongue weight, divide that number by .13. That will give a ball park number for your max trailer weight.