I went that route with my first born, removed the second system from the extra bedroom and turned it into a baby's room.
Our music taste is roughly the same with focus on jazz. I just cannot stand listening to jazz with headphones. These days, my headphone rigs are just collecting dust in the study room except the occassional use when I need to do some heads down work.
ASL is a good starting point, but I would not have suggested it for amp. HD600 are good. I have a pair w/ Cardas headphone cable. I also have a pair of HD650 w/ Zu Mobius cable. After doing some comparisons with several other cables side by side, I felt these are the best combos in my system. I have not tried many of the new offerings. I actually prefer HD600/Cardas when listening to my turntable than the HD650/Mobius combo.
As other have suggested, before shelling out any more money, check out www.head-fi.org and read! Good thing is the folks in the headphone community get together quite often, so you get to try things out first before you buy.
My alias there is "gundam91" as well. You can check out my headphone rigs there, and also some reviews I have posted in regards to headphone amps.
FrankC