For the 1188, you could put a 20 ohm 10 wt resistor in series with the 1188 driver. So, no matter how high the freq, there has to be at least 20 ohms present, right? The, in parallel with the 1188 and resistor, an 8 ohm non inductive resistor. So, now the whole thing looks like 8 ohms. So, come from the hot lead of the spkr's input terminal with a 25 uf cap (10 uf + 15 uf cap paralleled).