Interesting question. It is not too common to have 56kHz modulation, but clearly for Milestag like devices it is.
Unfortunately, we haven't used IRremote or IRLib for 56kHz yet. If I get some time later I will try it out on the oscilloscope.
The thing to consider is that 56kHz is just under 18 uSecs period (17.857 uSecs) or 9 usecs HIGH/9 uSecs LOW (@50% modulation). Given that IRremote uses 33% duty cycle by default, it would work out at circa 6 uSecs HIGH and 12uSecs LOW.
These timings are within the scope of Arduinos with ATMega class MCUs or better running at 16MHz.
If an example is not available for IRremote, then check out the article below which shows how to adjust things etc.
http://bluepichu.wordpress.com/2012/07/ ... uino-fast/
If you get it working, post back an example.
Also, to get the max range for your devices, generating high quality modulation with optimum duty cycle tuned for your receivers & data stream will get you the best range (plus really good optics of course).