We were in Argentina in May, and used ATM machines for all of our money exchange transactions. However, we never needed to withdraw a large amount at once--we generally got $100 - $200 US at a time, using our US ATM/Debit cards. As is the case elsewhere in the world, some ATMs have their own cap on the amount you can withdraw, so you may have to do multiple transactions. See
this thread for some recent information on FlyerTalk.
We were with a choral group on tour, and some of our members did have a difficult time with withdrawals because they had not notified their banks they were traveling, and the banks would not release funds. So don't forget to let your bank know you will be in Argentina, and also confirm what your daily withdrawal limit is at their end (they may be able to increase it for you if it is low).
As for using USD for transactions - some of our group did use dollars for small transactions - but if memory serves, that was while we were in Uruguay; and since I did not carry much US cash with me (other than a couple of $20s), I had no direct experience with this.
If you use the "Find" button at the top of this page and enter Foreign ATMs, or some similar phrase, you will find several threads with general answers to the how to get money issue.
Have a wonderful trip. We did not manage to get to Cordoba, although it is on my wish list for "next time". We loved the people, the food, the atmosphere, the interest in the arts and music. I'm sure you will love it.