Increase max audio buffer size

[mpharoah]

Instead of bounding the maximum audio buffer size to double the target buffer size, either use a larger value or let PulseAudio choose its own value. This will ensure that buffer underruns don't happen even if the PulseAudio server has a high latency.

Also, re-evaluate what the default value for target latency should be now that the buffer settings have been changed. Use a higher value if there's no noticeable lag.