Hi,
Apologies for the delayed response.
Unfortunately, I was unable to reproduce the issue. However, it would make sense that increasing the buffer size would affect the getDSPClock(). An alternative option may be using Channel::getPosition() this 'Retrieves the current playback position. You can retrieve the Channel from the ChannelGroup using ChannelGroup::getChannel(). You may have to dig down through a few channelgroup’s before you can find the right channel.
Hope this helps!