To convert RAW to discrete frequency the same as Muse Monitor, you will need to perform the following actions:
* hamming window
FFT is possible in Excel I believe with the Data Analysis pack installed.
Bear in mind that to create a spectrogram from a real-time data capture, you're talking about a MASSIVE amount of data, far beyond what Excel can handle. A single point in time should be ok to calculate, but I'm not sure how you'd do a spectrogram in excel to any useful resolution.
I would look into using something like processing.org if you want to do your own FFTs.
If enough people are interested, I could write a little windows app to convert the RAW data to a graphic file.