I am not KWAG and don't have his expertise but see if this applies to you. Don't necessarily blame it on having to go with 1150 constant bitrate on your Apex.
This audio problem fix may seem strange since you will hear a lot about demuxing and remuxing using tmpg or bbmpeg etc... I could be a solution in some cases especially if you get the file from someone else. I tried them all!!!
I have 2 Apex Standalone players ad700 and ad600A (used to have a 1500). I got the same audio problem and tried everything I could think of. I use DVDX (due to a temporary shortage of disk space and frameserve to Tmpg (now 2.55) to use the templates. To get rid of the audio jerkiness even though the movie was supposed to be 23.97 according to DVDX I selected 29.97 and it did an automatic pull-up. I then overrode the pulldown (unchecked telecine in tmpg) and made sure the framerate was shown as 29.97. I know this makes the movie larger but my 2 Apex players now accept the movies with no problems. What took me so long to figure it out is that the video looked so good I thought it was an audio problem. I became suspicious when I turned on the display on my Apex and the reported time was way off on all the clips (whether they were originally 23.97, forced to 24fps film in DVDX or telecined to 23.97 in tmpg). Now I can set the min and max bitrate compression without problem and the audio as low as I want.
It appears that my Apex players expect to get 29.97 as a rate.