Have you ran the hybrid and echo loss tests to adjust the lines?
I recently had a customer that had 8 copper lines on CenturyLink (ie. Qwest/US West) on a 5000, no matter what we did, how many times we ran the tests, and how we adjusted the lines, they constantly complained of poor audio, echo, low volumes, and crackling, but testing with a butt set was fine and pulling out the old 3M 965 put the lines in a marginal to unacceptable state with power influence very high and rather high loss levels... apparently the 5000 doesn't like that too much, we finally got the customer to switch to Midcontinent Communications (cable provider) for dial tone and re-ran all the tests in the 5000 and they are happy as can be now, and even though they were in a contract with CenturyLink for like another 2 years, after paying the ridiculously high ETF and fees they will still save several thousand dollars over 5 years.