I have owned both, liked both, and still have the J2. The funny thing is that I don't find them all that similar. The J2 is much more energetic, more detailed, more like the AJ with a slightly cleaner sound. To my ear, the F3 is ridiculously good--if your speakers are sufficiently sensitive. The J2 obviously brings more speakers into play, but it still needs 8 ohms. I hope that helps.
