When you add volume, you don't just impact a single muscle or muscle group. This increases the load on the entire body. Now, in my program description linked in the TOC (
http://www.elitefitness.com/forum/showpost.php?p=4764723&postcount=381) I do say that for more advanced trainees you can transition the 1x5 to 5x5. Doing it for chest is going to be less taxing than doing it for the entire slew of exercises (thinking the squat mainly and then adding in 5x5 for the rows) so it's something to consider just doing one.
All that said, you really should have a good foundation first and you can't do this midway through the program because it screws with the volume a bit. Your strength is obviously increasing pretty quickly, it's tough to make an argument that you require more volume when your bench is shooting up like this. The issue you are having with your chest is that the flat bench was not a core lift and lagged some of your other work, most noticably your dip. So when you dropped everything and went with a program that focused heavily on bench, even though you are getting better fast, you've had to take a step backward. I gave a pretty detailed analysis here:
http://www.elitefitness.com/forum/showpost.php?p=4870667&postcount=478
This will resolve itself fairly quickly but like I said, it's really hard to make the case that you require more volume when your bench is shooting up like that in 3 weeks - something is obviously working and working well. The strength increase is all you can control, size will come with strength and increased capacity over a decent rep/set range. You are doing that now but you are paying the price for having a weak realtive bench and over-relying on the dip. I guess you could have run this cycle with dips and not bench but you can't do less than bodyweight so it causes issues and it's not as good of a movement IMO but that's not too important.
My best advice is to be patient, don't screw with it and finish it out. You'll have a solid bench at that point. Run a 4 week program and incorporate your dips or whatever (you'll find a lot more parity between your dip and bench power after this cycle) then step back into a longer foundation style program like this one and work hard for a period.