Which processor? Linn, Rotel, Outlaw, Meridian?

Given what you already have, and having regard to used prices, I would go for the Linn 5103, which as you say is old, but good. I would also consider the Meridian. This presumes that you don't mind forgoing HDMI.

Linn makes the most sense.

Linn. Or a new Onkyo receiver

Since you say you will be using this system half of the time for music you may want to give more serious consideration to PLII as it is actually quite good and a huge step up from the older PL.

Just because you have a Linn amp and speakers I do not feel that the older Linn processor makes any more sense than your other options. I'm not familar with the Linn, but if it is as old as you imply I would not consider it as it will be difficult to sell should you not be happy with it. Most people buying surround processors want the newer technology at least up to a point.

After taking a very long look at many options I decided on the Rotel 1066, which I got virtually unused for $800. I could not be happier and recommend it highly. Don't be misled by the low price these go for. Rotel makes exceptional equipment for very reasonable prices and has been doing so for a very long time. I use mine with Classe amps and Aerial loudspeakers on the front end and a Rotel amp and Von Schweikert TS-150's for the rear. I use a Hsu VFT3 for a sub. In the past I used an older Meridian and a Proceed PAV. The Rotel was a big improvement and of course it could handle the newer surround formats.

You did not mention the rest of your system, but you might be able to put that extra $800 to good use if you went for the Rotel. What are you using for a DVD player?

You may want to read Robert Deutsch's review of the 1066 in the January '03 issue of Stereophile Guide to Home Theater if you have not done so already.

Although the Outlaw is a good bang for the buck I do not believe it can compete with your other choices, which have been designed by companies with far greater experience in both 2 channel and multi-channel audio.

Hope this helps...