Salam mate ..
For dum sound do check grounds of Pre and stereo amp also . Bro magus amp is lil overrated I think it gives 300-400wrms at 4 ohms max
It's been almost a week u had ur setup ,I think it's enough break in period ... Now connect your sub at 1 ohms to ur amp .... And keep the gain at 40-30 % for clear signal. You will feel the difference loudness and sPL .... Since u will meet usman he will do it for u .
For 4 channel amp get kenwood m846 at 9.5k but it still be giving 60wrms at 4 ohms but definatly good SQ.