Thanks for the responses. This past weekend, I have been experimenting with Particles. I love the principle behind it and it serves the purpose very well. I've been using the "manual" method as I couldn't quite grasp the "Utils" program method and getting chapter info from the web. All I can say is that it's a daunting task when you have more than a hundred mkv concerts.
So far, I've been using MediaInfo to get track names and chapter times. Then I manually have to enter these, one by one, into Particles. I'm hoping that future version of JRiver will help streamline this process. It appears the info is already in the mkv file since MediaInfo can pull it up. Wish JRiver could pull up that info as well, or allow importing it in an easy fashion. At the very least, allow entering multiple Particles at a faster pace like a spreadsheet, rather than going through menu items every time.
BTW, my main purpose is to create playlists of various tracks from different concerts. So gapless is not important to me.