Thanks for your response.
Have a look at the cited sources. The half a billion sum includes rental of equipment.
The cited study for CD purchases goes into their methodology. This paragraph is worth considering:
“The 2009 NHTS further yielded an estimate of 1,900 miles (3,058 km) driven by the average driver for shopping purposes, and, combined with fuel economy estimates from above, this produced a range of 0.03 to 0.14 kg CO2e/US$ shopping expenditure. For an average physical album cost of $15, this yielded a range of 0.5 to 2 kg CO2e/album, with a mean of 1.1. Thus, this validity check led to a slightly lower mean estimate and smaller range than the assumed method; however, a sensitivity analysis on the results showed that both allocation methods led to similar conclusions.”