No, because db is logarithmic. That's the key property that allows you to do addition instead of multiplication. Remember these are ratios here as well.

So the original example in linear units would be: We're reducing the signal by 63% in the this cable, and the gain through this amp is 199.5%, so the output is...

0.63 * 1.995 = 1.26

126% which is 20log10(1.26) db or around 2db.

-4 + 6 = 2 is a little easier to do.