I'm having trouble finding a comfortable marathon training/running shoe. I've been training in Asics Kayano 18 for more than 10 weeks but the balls of both feet are very sore after about 11 miles constantly. I have tried several different insoles all to no avail. I have tried running in my Brooks Cadence which are a little softer probably because they are more flexible but still they hurt after 12-13 miles also. The specialist at my running store suggested I try Newton's but with less than five weeks to race day I'm afraid of switching to this type of shoe which forces you to run forefoot which by the way is how I run until my legs become tired then I tend to land more midfoot. My concern is the break in period required for this type of shoe which probably should not be to long considering I already have the correct form. By the way I am 45 yrs young, 5-10",160lbs, run about 35-45 miles a week and a lifetime athlete. Any advice is welcomed.
I am not sure which insoles that you have already tried, but a footsmart gel cushion or metatarsal sleeve support might be worth looking into. I would not rule out a quality arch support either because sometimes that makes a difference with taking pressure from the front of the foot, depending on your circumstances.
Although you are around a month away from the marathon, you may want to go ahead with recommendation for the Newtons and just rotate them out in these final weeks of training with your Asics and Brooks. It would be a good idea anyway to have those three pairs to alternate the stress areas across your body. Then you can make a better choice about which pair to wear for the event.
Hope this helps and congrats on your first marathon!