Yes it does have series link. Do you need the music storage that the 78 offers? I have used it and find it to be a real pain to use and not very practicle. There is no display if the TV is off. There is no direct play button for music, and most annoyingly no random play button. You also have to decide each time you play music if you want to listen to music that you copied form CD onto the HDD or mp3 copied to the HDD. Surley this should not be a question that needs asking, just giv me a lis of everything.
Also if the DVD is connected via HDMI to the TV (only know this happens on Panasonics with Viera Link) and you turn off the TV, the DVD turns off too, even though you might be listening to music via the DVD on an additional amp.
If you do not need the music side, go for the DMR-EX768 instead, it's the nearest model to the one you have and about £80 or so less!