I have a 150 W subwoofer amp, and am considering connecting it to four shakers (two sets in series, connected in parallel). The first set of two are Pro (50W 4 ohms) and the other two are the regulars (25 W 4 ohm). With this configuration, I think the ohms facing the amp will be 4. Is the amp two powerful? Could I add another shaker in series to each set, and therefore make the final ohms 8. Will I notice any difference? I'm getting very confused about power and watts, etc now. Thanks.