Thanks for the feedback on your experiments at VHF with the Loop Antenna Amplifier +.
We specify the LAA+ to cover up to 150 MHz due to the low pass filter built into the head unit. In practice it will cover the marine band around 156 MHz with a few dB of loss.
There are two ways that you can improve reception of the VHF marine band with the LAA+.
The first is to check the polarisation of your loop. If the LAA+ is at the bottom of your loop then its horizontally polarised at VHF. For vertical polarisation you need to feed the loop from the side.
The second point is that at VHF the loop is acting as a full wave loop like a quad element. If you make the loop out of wire 1963 mm or 77 inches long it will be resonant on the VHF marine band.
If you try both these changes I'm sure that the loop antenna will out-perform your discone.