@djohn It's interesting to hear of Scott Franklin's recommendation here. I had the ARC SP-10 for 8 years before I switched to the LS5 II, and then the III some years later.
My final showdown with the SP-10 was the MFA Luminescence at a dealer in the mid 1980s. I remember that session vividly. The Lummi provided bass extension and authority but lacked much needed extension on the top. The SP-10 did not at all have the bass authority or portrayed power in the lower mid, but the SP-10's dynamic contrasts were incredible. The Lummi's strengths were the lower octaves, the SP-10's were in the upper octaves, but both lacked detail in the very top. The Lummi was more laid back at the speakers with the SP-10 out into the room. I ultimately bought the SP-10, but the Lummi was special.
And then in the mid 90s, the final showdown for an update from the SP-10 was the LS5 II vs. the Sonic Frontiers SFL-2. The differences were very much the same, and no surprise.....it was the same designers head to head again. The LS5 did the 3D magic with greater ambiance, but it lacked the authoritative power of the SF. Notice that I do not use the word, "better". Both models improved from their older models in the previous shootout, but compromise was still high.
All these years later, I felt that the forward presentation of the SP-10 and LS5 was not natural. The ARC's forward presentation can be appealing and addicting, but after 15 years with the ARC products, once I heard a system with the sound back at the speakers and behind, and extended into the top octaves, there was no going back. The 1980s Counterpoint SA-5 auditioned 10 years ago confirmed this.
Almost 30 years after the LS5's creation, so much refinement has come along where the compromises I have described above no longer need to be made. If someone is willing to pay $2500ish for an LS5, and put another $1k into an update, there are just too many models available on the used market today at this price that offer a multitude of refinements.
Oh, and I used a Classic 60 loaned by a colleague for almost a year until I dropped in an ARC VT130 amp in the late 90s. Wow, wow, wow, lovely. Ahh, the good ol' days.
John