You may want to disable all other messages produced by the receiver and ensure that RXM-RAWX messages are enabled - you should be getting continuous stream of messages with B5 62 02 15 header.
u-blox does not provide conversion software.
The following software was given a good review by u-blox customers:
Novatel - Waypoint: http://www.novatel.com/products/waypoint_pps.htm
You may want to check with RTKLIB and TEQC to make sure they can support multi GNSS messages from u-blox M8 receivers.