Hi. I recently got the BMW Alpine kit put in, because the standard stereo sounds so muddy I couldn't bear to listen to it. Mine works well, though they did have to do software upgrades and the like. I am very happy with the results, and it is much better than the Alpine kit I had put into my 2006 E90 (sound was less balanced on that one).
I would definitely take it back in and have them look at it.
Did you have it done at Adelaide Motors?
'05 E90 325i 6sp Man SG 118,032km on the odo (retired) | '06 E90 325i Step SG 121,021km on the odo (retired)
'08 E90 325i LCI Step SG 130,024km on the odo (retired)
'13 D30 328i M-Sport Step | Estoril Blue | Black/Aluminimum | Pro Nav | Xenon HBA | Lane Change Assist 1,760km on the odo