I have a G11 with the Patima aluminium housing and use my "old" 2007 Inon D-2000 strobe with excellent results.
Basically There are 3 options regarding Inon strobes:
1. get another S-2000 for size and/other weight reasons.
It seems that it has the same power as the D-2000 and it's small size looks good with the G11.
2. trade or sell the S-2000 and get 2 D-2000
The D-2000 has two strobe tubes, weights almost the double of the S-2000
3. Trade or sell the S-2000 and get 2 Z-240 because they are slightly (GN4) more powerful but that is underwater not much in distance.
You can see and confront them here: http://www.inon.jp/products/line_up.html
I see no reason to buy the Z-240 for expandibility reasons as modern, advanced, optical triggered slave strobes like the S/D-2000 or Z-240 an guarantee perfect exposures with virtually any camera and housing on the market able to fire and let pass the internal strobe. Only backdraw is that they need the flash from the internal strobe to work and that can be a problem with Ikelite DSLR and some aluminium housings without optical strobe "window".
Depending on your budget and personal needs i would go with the D-2000 as i find the Z-240 not really woth the extra money and the S-2000 is only 1 strobe tube providing a slightly oval beam.
Hire some further articles regarding the Inon strobes:
Difference S-2000 D-2000 http://reefphoto.com/tt/index.php?action=kb&article=11
Inon Settings: http://reefphoto.com/tt/index.php?action=kb&article=7
Chris