The signal going into the Eros should be over 2mV at the barest of minimums. A 0.18mV cart is ultra low output, so a 1:30 or a 1:20 step-up is necessary. For the S1 in particular, I would use the 1:30 Sowter and change the loading resistor from 47K to 150K.
Some of the Denon MC carts are a little strange in that they will have both low output and a higher than expected recommended loading impedance, so some tweaking is often in order to get these to sound their best.