finding amplitude of a specific frequency

[kamocat]

I'm trying to make a DTMF decoder with LabVIEW. However, I want it to be able to handle the possibility of several signals overlapping, instead of just assuming it's the first one it finds.
To do that, I need to find the amplitude of a 7 predefined frequencies.

My question is, what is the most efficient way of doing this?
Should I separately filter out each frequency with strict tolerances, and then analyze each filtered waveform to find the frequency of greatest amplitude?
(Doesn't sound very efficient)

Or should I use "Extract single tone information.vi" without filtering, and just enter the frequency I'm looking for in the "advanced" cluster? (I'm assuming a +- 5% band would be tight enough)

Or should I look for the highest peak in the waveform, generate a waveform of the desired frequency, and somehow correlate the two waveforms? (say, subtract or divide, and then look at the remaining variation in frequency)