So, I checked out a couple of the converters that were on the "top 10" list from
@Julian's url. First, I tried Switch Sound. As the author in the top 10 list suggests, it's not totally free. It's a 15 day trial, but I'm not against paying for something if it's worth it. The reason that I chose Switch Sound first is because it mentions that it has sound leveling. In my opinion, the sound leveling didn't work, but maybe the songs that I had in mind to have the software fix were within a tolerance range that the software considered acceptable. A few things that I learned when using the trial software. If you want to purchase it at time of initial trial download, it's $25. The trial software is good for 15 days, but I also learned that there are other limitations that are not mentioned up front, like a 100 song limit (then the sw stops working), and you can only convert 5 songs at a time (pita). Once the trial abruptly ended when I hit the 100 song limit, I was offered the software for the purchase price of $16.97, as opposed to the original $25 ... hmmm.
Not convinced that Switch Sound was worth paying for if there is free-ware that will do the same thing, I tried MediaHuman Audio converter (also from the top 10 list in Julian's url). It's free, faster, and has no limitations on the number of files that you can process at once. It doesn't claim that it has sound leveling, so I didn't test this aspect of the software. This is the software that I'll be using in the future.
In parallel, I looked at the Google Play store to see if I could find a music player that could play m4a and wma files. I tried a couple free ones. PITA software that didn't work as I expected. They only played mp3 on my phone, so I cut my losses and I'll stick with the original Google music player, and just convert my music to mp3. That way, I'll have my music available on a usb flash drive for the Connext on the boat.
So, if you're looking for simple to use, batch-capable, fast, and free software to convert your music files, MediaHuman Audio Converter is my recommendation.
Thanks to Julian for providing the top 10 list.