I have a faulty Astell & Kern T5P that I never returned because the warranty had expired. They worked fine when I bought them but after a while the left channel of the T5P stopped working. I also own Sennheiser HD700's and though I liked the sound of them I rarely used them. I found them to be very uncomfortable, i was always having to adjust them on my head every 5 minutes. I hardly ever use them because of this but I knew that the HD700 has easily removable drivers and I thought maybe I could remove the drivers and put them in the T5P's. I prefer closed-back headphones and I was curious to hear how HD700 drivers would sound in the earcups of T5P's. So I decided to do this mod. As the HD700 drivers are small (40mm) and light, a bit of Blu Tack is all that is required to keep it firmly in place The resulting sound of HD700 drivers in a closed-back design, is very fascinating. overall they sound allot more analytical than they did before. This little DIY project of mine has puzzled me as to why Sennheiser won't make a closed-back alternative to the HD700 or HD800, I really think Sennheiser should cosider it.