In my experience there is a "house sound" that is similar throughout the RSA line. I've spent time with: Hornet, Raptor, Apache, and B-52. (I haven't heard the Predator or the SR-71 that I can recall.) For me, there is a very distinctive RSA sound that is different than the other house sounds that I am most familiar with (RSA, Singlepower, and Rudistor). I have most often listened to RSAs with Edition 9s and Senns 600/650, but I've also spent some time with the K-701 and R-10s and Ath-AD2000. Of course there are differences between RSA portable amps vs desktop, SS vs tubes, and SE vs balanced, but they all sound like different presentations of that same basic house sound to me.