[Kuroshima]

Well, the ST table works like this:

ST      sw     thr         nsw        nthr 
10      1d    1d-2         1d6         1d2
11    1d+1    1d-1         1d8         1d4
12    1d+2    1d-1        1d10         1d4
13    2d-1      1d     1d6+1d4         1d6
14      2d      1d         2d6         1d6
15    2d+1    1d+1     1d6+1d8         1d8
16    2d+2    1d+1    1d6+1d10         1d8
17    3d-1    1d+2     2d6+1d4        1d10
18      3d    1d+2         3d6        1d10
19    3d+1    2d-1     2d6+1d8     1d6+1d4
20    3d+2    2d-1    2d6+1d10     1d6+1d4
and so on

Basically, use this conversion:

1d-3->1d2-1
1d-2->1d2
1d-1->1d4
1d->1d6
1d+1->1d8
1d+2->1d10
1d+3->1d12

If the bonus exceeds +3, and there is more than one dice, use this table:

2d+4->1d12+1d8
2d+5->1d12+1d10
2d+6->2d12

This has the funny side effect of turning per die increases into increased dice sizes:
+1/dice->Increase all dice by one step

Beware, this will make damage more random, while it keeps the average damage the same. This will mean that when before, the armor protected almost all the time, and sometimes left a small amount of damage in, now the armor will negate more attacks, but when it gets penetrated, the chances that the damage is significant exist.

EDIT: basically, this is an alternate convert to dice. Instead of referring to the tables above, the rule is simple: Get Dice+adds as usual, and then for each +3, convert 1d->1d12. Then, if you can, "spend" a +2 to convert 1d->1d10. Then, if you can, spend a +1 to convert 1d->1d8. If you have negatives, every -1 converts 1d->1d4, and if you have leftovers, every -1 converts 1d4->1d2. Any leftover -1 are applied to the total.