You don't need a meter to tune and you don't need to be a proffessional either.
What is your source, a cd player? Or carPC?
If you are using the RCA inputs on the PXA, read the manual for the processor and you will find a little section that talks about how loud to turn the volume up on the source unit. On my processor (alpine PXA-H510) you turn the volume level on the processor right down to 0 and then adjust the source volume leve till a little "OVER" flashed on the controller unit, once you reach this, turn the volume DOWN a tad more.
DELETED this section, just read the tutorial, its very helpful. http://www.mobileelectronics.com.au/...howtopic=35875
Make sure you read the section about low pass filters on sub woofers and high pass filters on speakers.
When you are setting the sub gain on the amplifier, adjust the sub volume on the PXA controller unit to around 5 or so, this means you can adjust the sub to be louder or more quiet.
Time correction is also another one of the nice features of these units, read the user manual and you will find out all about it. Basically you are manipulating the sound so that when you sit in the drivers seat it sounds like you are sitting in the middle of the speakers. Since speakers are locatated at different distances it can "seperated", but time alignment (time correction) fixes this. It is amazing how much difference it can make despite how skeptic some people are.
Adjusting the equilizer is hard, but just play around with it lots. Read the manual for instructions on how to adjust the equilizer for all the difference speakers and "BANDS".
The problem with getting someone else to do it is that it may sound good to them but not to you. Its all about personal preference and opinion.