states that the 1040 can monitor up to 100 concurrent RTP streams. If you go over that number you start to see false alerts such as jitter alerts and dropped packets. We had one of our units monitoring a couple of Class C addresses (before we found the supported number of RTP streams). This was at a call center. We were pulling our hair out trying to find the source of the non-existent issues.
Limiting the 1040 to 100 RTP streams cleared up the false alerts issue for us. This, unfortunately, meant that we couldn't monitor even an entire Class C space (it was a trade off, efficient use of IP address space or no real-time monitoring). Monitoring 60 current streams shouldn't make the 1040 sweat.
An yes we monitored both TX and RX (though I'm not absoultely sure that's necessary).