http://www.kenwood-electronics.com.my/imanual/KDC-MP5029.pdf#search='Kdcmp5029'
Look at the manual, your HU have 2 pre-outs, front and rear. Seems like you have to check back all the connectios, from HU to crossover to amp. The best solution I can think of is HU front > XO > amp > speakers, HU rear > XO(sub) > amp > sub, so you will need total of 4 RCA cables. Maybe the fellow connect it wrongly, XO speaker go to sub and XO sub go to speaker..