Originally Posted by RonRizz

Trust your shop, if it is reputable, like you say.
Ask them if they bypassed the bose amp, or used a harness to feed into it. Its not likely they bypassed it, but it is possible, and would explain your loss of volume.
Im curious about the 2 fuses for the HU, probably the 2 amp on the switched 12v side, and the 10 amp on the 12v constant side. ask them why they only used one. This would not affect your volume issue, however.
Many companies do offer Micro amps, Some are as small as a pack of cigarettes, and have decent power ratings. NVX is one that comes to mind.
Good luck