I have been inserting the 8mm sound 2 or three times a day for the past week, and it is still a little tricky to get past the glans without first using the 7mm. I had been becoming frustrated that, as I saw it, the 8mm sound wasn't actually stretching my meatus, but merely deforming it, and that I could potentially end up stuck in a rut.
I also have to admit to reverting to KY jelly for lubrication, I was wrong. As the sounds are quite tight, saliva was simply not up to the job, it dried far too quickly, and although the KY does become quite sticky when it dries, it does last much longer, and is much easier to reapply than saliva.
So, yesterday evening, I experimented a little. I got the complete set of sounds out, and tried inserting the smaller ones two at a time - potentially risky, I admit, but I've never been a very patient person. I had a couple of dodgy moments when the narrower sounds poked me a little, but I was eventually able to insert the 4mm sound AND the 7mm at the same time. This means my meatus is able to accomodate 11mm, unfortunately, that is in height not width. In other words, the urethra, as it passed through the glans, is basically oval in shape not round, and try as I might I was still unable to fit the 9mm sound into me.
The next day I was disheartened, and spent most of the day trying to devise a way of stretching my meatus continuously, in the same way that people insert devices into their ear-piercings to stretch them out. The trouble is of course, any such thing would have to allow urine to pass through, and I am worried about leaving something in my penis for too long in case of infection or tissue damage.
I returned home this evening, and gave it another go with the sounds. Using the different sized sounds I tried manipulating the very entrance to the urethra to try and stretch it a little, and also tried coaxing the 9mm sound further in (it has gone into the meatus, but it stops short of the meaty part of the glans). After some time I had pulled and prodded myself and caused myself a lot of discomfort, but I admit it had released quite a few endorphins into the system, and although I wasn't comfortable I wasn't in any real pain. So I decided to try inserting the 9mm sound slowly, by lubing it up a lot, and applying a firm and constant pressure on it. I very slowly managed to work it about a centimetre into me, and each time I applied pressure my glans protested quite strongly.
After a few goes, and a LOT of lube, I was pressing the sound into me when it suddenly gave and entered the urethra proper. It hurt considerably, and I had to remove it again almost as soon as I had realised what had happened. After a massive adrenalin rush, I realised that the flesh of the glans wasn't damaged, and that it had merely given in to pressure. While I still had the endorphins in my system I did the same insertion a few times, managing to last to around 6 or 7 seconds with the sound inside me, before the pain became too much to bear.
I didn't want to risk my luck, so I washed my penis (squeezing quite a bit of KY out of me) and hygiened my sounds. That was earlier this evening, and my penis feels completely normal, it doesn't hurt at all and feels fine when I urinate.
I am buoyed up by this little development, and although the 9mm is still going to be a big hurdle, I know for sure it is one I can jump.
As a small addendum, I have started drinking cranberry juice. I read somewhere that it is very good for cystitis, and I figure it might just help keep my urinary track healthy. If it does nothing, I haven't lost out, because hey, it's fruit juice!