My pick is C.
What was as remarkable as the development of the compact disc has been the use of the new technology to revitalize, in better sound than was ever before possible, some of the classic recorded performances of the pre-LP era.
A. What was as remarkable as the development of the compact disc (We have two different tenses – ‘was’ and ‘has been’ – wrong)
B. The thing that was as remarkable as developing the compact disc (tenses again; also ‘the thing that was’ not very clear and awkward)
C. No less remarkable than the development of the compact disc (good)
D. Developing the compact disc has been none the less remarkable than (wrong comparison ‘none the less … than’, also the meaning has changed)
E. Development of the compact disc has been no less remarkable as (same as D – wrong comparison ‘no less… as’; also the new meaning implies that development of CD was more remarkable than the use of the technology – but the meaning of the original sentence is the opposite).