Linn vs Audio Research

Linn is kind of like a Corvette; ARC is like a Cadillac. I'd go with the Corvette---it's a much better car.

Linn is more like a Saab than a Corvette.

Marc, I've owned much of the gear you are considering. I've been able to listen extensively to the others, except the Apertura speakers. The options you mention would really be moving in different directions. If you, like myself, are a fan of Linn's ability to resolve inner detail and preserve the PRaT (pace, rhythm and timing) of music, you should stay with Linn. Audio Research gear is good, but has a different character and flavor. Although ARC components are some of the least "tubey" tubed electronics, you will still find that they add warmth to the midrange, roll off the treble somewhat and smear the bass timing/control in comparison to the Linn gear.

My advice would be to stay with Linn. Go with Aktiv Espeks powered by three 2250s. If you haven't already, consider upgrading to the Linn Silver interconnects. They make a nice addition to an all Linn system. Post your system sometime to let us know how it turns out!