unison 845set integrated driving maggie 1.7?

SET amps can only really shine above 6 Ohms and above 93db. For your maggies I would buy a Crown XLS 2500 (cheap, but very very good!) and invest the rest in the very best source you can afford (Resolution Audio Cantata MC, DCS, TotalDac, MSB, Berkeley ...)

The 1.7 has a sensitivity of 86db/2.83v, however since it is 4 ohm, that is 83db/1 watt. If you are listening nearfield to elevator music at low volume, it should be fine. Now factor in a little more distance from the speaker, a little more volume, music with more dynamic range, and it is very likely the power needed on peaks will be more than 24 watts. IMHO, this combination should be avoided as there will be a risk of damage.