Would you still wish to be able to listen to music whilst using the text viewer ?
Because your choice is one or the other - you could change the text viewer to grab the entire playback buffer to use, which would stop the ability to play music at the same time as reading, or you live with the size of the buffer as it is now.
The third option is to make yourself a custom build with a larger plugin buffer (but this affects ALL plugins, and not just text viewer) at the expense of the playback buffer.