Amplitude problem by puting 5 FIR in a row
Look at the power spectral density of the signal prior to application of filter b5.

If you filtered white noise with two filters, one with a bandwidth of 11 MHz and the other with a bandwidth of 60 MHz, and both with the same passband gain, then indeed the difference between the power of the two output signals should be about 10*log10(60/11) or 7.3 dB.  But if, for example, your signal was already bandlimited to the 11 MHz bandwidth of filter 1, then there would be little difference between the output powers of the two filters.  A signal with a more complicated spectra (e.g., signal is within 11 MHz, but broadband noise exists) will be somewhere in between.

Also, if you are trying to compute the power of the signal in dB, you would not have a sqrt in your 10.*log10(sqrt(I.*I + Q.*Q)) equation.