Yea, tell your friend to always be open for suggestions...Because quite frankly he doesnt know shit about car audio...Look, the subs dont see a load, the amp sees a load...Your amp is only 4 ohm stable while bridged and you are running 2 ohms...And if you have a so-called "mono" amp, you would know that you cant "bridge" anything...Please listen to your friend...or find a new hobby...
EDIT: That may have sounded harsh, but look you are going to fry something and hurt your equipment, the vehicle, or maybe yourself...Either get weaker subs, or get a stronger amp...I recommend you get a mono amp that does 800 rms@ 2 ohms...