Your assumption is correct, it sets the volume to whatever it was at the last shutdown. It is fairly simple to change it to use a fixed volume yourself. Just follow these steps:

• Open the file "ttsclock" with a text editor. (If you use windows notepad then be aware that line breaks will appear as little boxes. Don't remove any of these boxes or add any returns.)
• Find the text "/drive0/var/setvol"
• Change it to "/drive0/var/setvol ##" (no quotes, where ## is a percent from 0 to 100 for the volume level)
• After saving this file, you can use the automatic installation script to reinstall your modification, or if you know how to manually upload and set permissions you can just update this 1 file.
  

The TTSClock program currently has no daylight savings code, so while the empeg player app will automatically adjust the time during time changes, the ttsclock program won't. Maybe I'll make an updated version before the next time change to have automatic daylight savings time changes.