see the top middle of pic len , looks like plenty of room for an 8-10mm drill bit to go through???
sorry i didnt post earlier to save you all this hassle but assaid before you still did a good jod..
Well yes now with hindsight and being told that you can pull down the internal end to drill it!
But hey I'm more than happy with the job I did and it gives me capacity for maybe another set of speakers!
YES I may well have additional plans now!