If your laptop is still under warranty then this is something they have to repair for you. It sounds like a hardware error, not sure about the actual fault but two speakers burnt is weird. (Especially if you keep the volume near 60-70% of the max volume)
Still if the laptop is out of warranty then dissasemblying is required. The information required are all give to the Service manual of th DV6000 provided from HP itself along with the part list and coding of the new set of speakers you need.
The process is not hard actually for this model. It can be done fairly easy. (in other laptop a complete disassembly is required which is very tough task)
The manual you will need is the one below. (Simply left click) http://h10032.www1.hp.com/ctg/Manual/c01035677.pdf
At page 146 you will see how the speakers are removed. Also follow the instruction on the quoted previous sections.
The part number of the speakers is 431447-001 and it is mentioned at the same page.
The part costs around 5$ used from Ebay :) If you dont believe me check it out yourself :) http://cgi.ebay.com/HP-DV6000-SERIES-SPEAKERS-431447-001_W0QQitemZ180230305257QQihZ008QQcategoryZ16145QQcmdZViewItemQQ_trksidZp1713.m153.l1262
Many regards and I hope you can get your precious laptop working again as a charm :)