[The HACK]

Go and do a couple of stops and activate the ABS pump, then bleed and see if that helps.

Also, if your street pads have worn down further than the track pad, there may be some "retraction" of the pad causing the pedal to travel further than the track pad. I don't know how exactly to explain it.

Lastly, street or organic pads are simply "softer" than high metallic content track pads, requiring a little more pad pressure to supply the same "bite." If you got used to the track pad's pedal stiffness then the street pad may cause the pedal to feel a little "softer."

Or it could be a combination of all of the above.

And you may not like to hear this, but I have friends with E36 M3s that swear that their brake pedals are never the same after their first pad change or fluid, no matter what they do. Something about BMW brakes I guess.

There are some extra steps that i do SOMETIMES before I swapped over to fixed calipers to bleed/flush BMW brakes. Usually I use a pressure bleeder like the Motive bleeder attached to the reservoir so I would never run out of fluid, but ALSO if I ever experience a soft pedal after a bleed/flush/pad change, I elicit a friend to do the pump/open/close/pump routine until the pedal is firm again. Just make sure the pedal never goes all the way to the floor when you pump and you're golden.

One LAST thing (I'm just full of last things) to add. Usually, especially back in the sliding caliper days, as soon as I'm done with the pad change, even before I switch the car on, I would pump the pedal until it's firm before I turn the key. Don't know if this will help, get in the car with the keys out, pump the pedal a few times until it's rock solid, then start the car. See if the pedal feel returns. Don't know why, but this often times work for me that, completely out of habit now, I always pump the brake twice before I start ANY car (it's also just to check and see if the brakes work before I start) even the electric, which is absolutely not necessary.