Unfortunately, Pa Landlord/Tenant Laws are not very specific at spelling out who bears responsibility for Mitigating Losses.
However, that doesn't mean the landlord shouldn't try to find a tenant to replace you or be open to accepting someone that you find to replace you. In fact its probably in his best interest to do so. The reason why is because just because you move out with 6 months left on the lease, and the landlord takes you court doesn't mean the Judge will automatically award him 6 months of rent from you. More than likely he would only get a few months worth of rent. Then a few months later, he would have to then come back into court and file another claim against you as the months accrue for the remaining unpaid rent.
The only way he can get all of the remaining 6 months of rent all at once is if he has what is called an Acceleration clause (google it) in his lease stating, should you Break the Lease all of the money for the term/year would be due and payable at once. The question is would it really be in his best interest to let the property sit vacant for six months and then have to waste time and money suing you when he could have the property rerented out almost immediately? Only the landlord can answer that.
It sounds to me, that he already has at least thought about it and that may be why he has some kind of penalty clause in his leases that state you must pay back any discounts given as well as a 2 months lease break fee. It doesn't sound like there are any issues with the apartment itself or that the Landlord is breaching the Lease therefore you are breaking your lease without cause.
I know its your decision but If there is only 6 months to go you might want to think about hanging in there. Or if you are really unhappy and are going to leave no matter what, I would try to work out something thats a win win for everyone. Perhaps you could offer to pay one month penalty and in addition to advertise for the landlord to help find a new tenant to replace you prior to moving out so that the landlord loses no money. If you approach the landlord making it look advantageous for him then he might be open to it. You wont know unless you ask. Good Luck