Before you give up on your Lamm, I would look to the amp. I would think the 14.87db gain provided by the L2 should be enough with that amp. From Rowland's website on the Model 5 specs;
Overall Gain Selectable: 20, 26, 29.5, 32 dB
Sensitivity 36 mV, 1 watt, 8 ohms
Input Impedance Selectable: 100k, 20k, 600 ohms
It appears you can select your gain (maybe by internal dip switches or jumpers?) and also your input impedance. Start by checking the input impedance. Although the output impedance of the Lamm is stated as "nominally" 130 ohms, the actual output impedance could be much higher at low frequencies. You should make sure your amps are not set at the 600 ohm input impedance, then try both the 20K and 100K ohm settings to hear the differences. You should also check to verify your amps are not set at the lowest gain setting, and adjust the amp's gain setting as needed to achieve the best sound. Hopefully, you can resolve the problem without the expense of changing equipment. Good luck.
Overall Gain Selectable: 20, 26, 29.5, 32 dB
Sensitivity 36 mV, 1 watt, 8 ohms
Input Impedance Selectable: 100k, 20k, 600 ohms
It appears you can select your gain (maybe by internal dip switches or jumpers?) and also your input impedance. Start by checking the input impedance. Although the output impedance of the Lamm is stated as "nominally" 130 ohms, the actual output impedance could be much higher at low frequencies. You should make sure your amps are not set at the 600 ohm input impedance, then try both the 20K and 100K ohm settings to hear the differences. You should also check to verify your amps are not set at the lowest gain setting, and adjust the amp's gain setting as needed to achieve the best sound. Hopefully, you can resolve the problem without the expense of changing equipment. Good luck.