When we set up a BPM fader with a range of 0 to 600 and slaved it to a MIDI controller and then sent 127 on that controller, we are getting 600 in the BPM fader.
It could be that Max is not sending 127 when the input is 600. (In fact, if we send 126 to Kyma, we see a value of 595.28, which is very close to the value you were seeing when Max was sending 600.
You can check to see what Max is sending by using the Kyma Event Log (choose MIDI from the Configure drop down menu of the DSP Status window and then click the Show MIDI Messages button).
If you can get by with a smaller range, it might be better just to offset the BPM values and not scale them. For example, you could set the range of BPM to be 473 to 600 in both Max and Kyma and then you would get the same values in both.
Alternatively, you could send a 14-bit controller from Max and then you should have enough accuracy to keep the same BPM in Kyma.