no amp that only puts out a hundred watts is going to be able to take the output of the S9 without some serious modifications.
more than that, there's no point in stepping up to only that much wattage.
to increase your signal on someone else's receive meter by 1 S unit; you will have to increase your output by 4x.
that means if you are deadkeying 10 watts and swinging to 50 watts (about the output of the S9), and hitting someone's receiver at an S-5 swinging to an S-6; you will have to deadkey 40 watts and swing to 200 watts to hit them with an S-6 swinging to an S-7.
thats just the way our physical universe works.
now, stepping up to an amp like the Texas Star DX500 will give you about a 100 watt deadkey swinging to about 450-500 watts, and it will handle the output of the S9.
still not quite 2 S units increase from just the barefoot S9, but hey, 2 S units is still pretty good.
after that, it gets very expensive to get those next 2 S units as im sure you can see.
can you say 1600 watt deadkey swinging to 8000 watts?
hope this helps,
LC