Greetings,
ECW files generally are already highly compressed. You could try other high quality compression algorithms such as JPEG 2000, JPEG, or if you have the license for it SID. Note that these compressions are lossy, meaning you will lose some pixel information (usually not visually distinguishable). Changing the compression quality (e.g. jpeg 75 to 35) will result in a smaller file on disk but also degrades the visual image quality.
When you say the files are huge, is that the dataset properties size or the actual size on disk? The dataset properties size will be uncompressed size and does not always correlate to the actual size on disk.
Hope this helps.
Robert