Rumba,
If you are using the matching MIT V2.1 rca int with switchable impedance networks,(V1.1,2.1,3.1 etc). I found the 150S2,180S1 and 250 sounded best in the medium position,(40-100k). The 150,180 and 250 per Spectral have a 100k input impedance. The 360 has a 10k input impedance. The specs for the switchable impedance networks are low (5-50k),medium(40-100k), or high(over 90k).
If you are using the matching MIT V2.1 rca int with switchable impedance networks,(V1.1,2.1,3.1 etc). I found the 150S2,180S1 and 250 sounded best in the medium position,(40-100k). The 150,180 and 250 per Spectral have a 100k input impedance. The 360 has a 10k input impedance. The specs for the switchable impedance networks are low (5-50k),medium(40-100k), or high(over 90k).