BMW E82 sound upgrade issues

[JPE82]

hi folks ,

ive a E82 118 d 5 stock speakers 2 door 2 parcel and 1 sub ,

ive since upgraded to
2 speakers and 2 tweeters in parcel shelf
2 speakers and 2 tweeters in the doors
1 sub to 2 subs under the seats

all HK , running of a pro head unit

im now getting a little bit of crakerling and a mid volume , now 2 points

1 is this as ive doubled the amount of speakers on the stock amp ?

2 dose a HK amp be a stright swap or will i need to code some thing ?