Volt wise. When you're mathing out your strings you add the VoC rating of each panel together for the total voltage. Those 100w panels are usually in the 20-ish VoC rating, so 6 would be about 120v-ish. Add 20% fudge factor for really cold weather and you're somewhere in the 145v-ish range which is the top end of what that unit can support.
EDIT: Looking at the specs it's 22.3VoC for the panels, 6s would be 134v (still within the 145 happy range) but if it gets really cold you could get as high as 161v (too high!) which would be too much. How cold does it get where you live? Below freezing? WAY below freezing? Just barely freezing? Never that cold?