why we can?t get much more play data in win7 and win8 system?

We develop USB sound card driver by means of Avstream.

We need to obtain much more data when playing, because the speed of USB sound card?s clock is much faster than that of window?s. We can obtain much more audio data that we need in XP system. However, we can only get twice the normal audio data in win7 and win8 system, and after playing several hours those data will reduce by half.

Questions:
1, why we can?t get much more play data in win7 and win8 system?
2, what I need to do if I want to get more play data in win7 and win8 system?
3, if I can only get twice the normal audio data, how can I ensure those data will not reduce by half even after palying several hours?

We develop USB sound card driver by means of Avstream.
We need to obtain much more data when playing, because the speed of USB sound card?s clock is much faster than that of window?s. We can obtain much more audio data that we need in XP system. However, we can only get twice the normal audio data in win7 and win8 system, and after playing several hours those data will reduce by half.
Questions:
1, why we can?t get much more play data in win7 and win8 system?
2, what I need to do if I want to get more play data in win7 and win8 system?
3, if I can only get twice the normal audio data, how can I ensure those data will not reduce by half even after palying several hours?