Hi John, hopefully i can help you here to save some money. firstly, your headphones are fine and i think you should definately replace the amp before moving on. i have owned several pairs of headphones in my time - sr125(not the i version), sr325i, and senn hd650.
i have to say that of all those the sr125 were my favourite - testament to this is the fact i still own them. i did a/b comparisons with them and the other models metioned and found them far better than the much more expensive hd650s and could not find any real difference (other than the price) with the sr325i's.
i have used two different headphone amps in my time the graham slee solo v3 and the creek obh21se. i found the creek much more to my liking and it was also cheaper - seems to be a recurring theme here that more $$$ doesnt always equal better sound...
anyway, just thought id share that with you so you might try to get the best from your existing cans before its too late! and yes there is bag loads of detail to be had from your cans when fed through the right amp.
goodluck
listen with your ears and your heart