Dear Lewm,
i tried both ways, a switch with relais (Manley switch) and the silverswitch of Dertonearm. While the Manley is a really good design I stayed with the UNIswitch. Of course you always have a degrading when putting units in between the lines but this unit keeps the qality in a very satisfactoy way.
Another option is going for the EMT JPA-66 with four tonearm connections (one MM, three with inbuild SUTs) and two line connections. This is in my eyes the most versatile and best sounding tube phono pre, also and especially regarding MMs.
i tried both ways, a switch with relais (Manley switch) and the silverswitch of Dertonearm. While the Manley is a really good design I stayed with the UNIswitch. Of course you always have a degrading when putting units in between the lines but this unit keeps the qality in a very satisfactoy way.
Another option is going for the EMT JPA-66 with four tonearm connections (one MM, three with inbuild SUTs) and two line connections. This is in my eyes the most versatile and best sounding tube phono pre, also and especially regarding MMs.