Best line stage $600 or under?

I have a (mostly) LP-sourced 2-channel system in the living room. A couple months ago I got a Cambridge 640p phono stage to replace my wheezy old Amber Model 17 preamp. This kicked off a flurry of experimentation and a spate of other upgrades. I tried the Cambridge phono into several other line stages, including a 1st-gen. Parasound ZPre, an '80s VSP Labs Straightwire II, a mid-'90s Class A JFET Hafler Series 915 (claims a bandwidth of 8-170KHz), and a 7.1 ch. Outlaw 950 Pre/Pro.

After switching all these preamps in and out, I found: The ZPre (again, 1st-gen, not a v2) sounded "OK," but didn't really pull me into the music. The Hafler I can't quite get my head around. Sometimes it sounds full and involving, sometimes it sounds closed in. Image specificity is good, bass is full. It seems to sound better with CDs than LPs, and in the case of most other preamps, I liked LP significantly better.

The Straightwire is very fast, open, detailed, but by no means sparse, etched, or thin-sounding. It would probably be my line stage of choice (this thing was something like $1500 in 1985) except it's showing its age and the left channel often ducks out.

That leaves the Outlaw. Frankly, when you use the Outlaw simply as a 2-channel or multi-channel line stage in analog bypass mode, it comes scarily close to the VSP Straightwire, plus it has remote control. I mean, it's fast, linear, extended, detailed, and clear, without being grainy, edgy, or etched-sounding.

There's just one thing: I'm only using about 1/10 of the circuitry inside this huge 7.1ch pre/pro to get the line stage and remote I'm looking for. The Parasound ZPre's size is pretty representative of the amount of function I need (4 inputs, headphone jack, remote, solid build quality, detachable power cord), but it leaves me cold. If the ZPre v2 is everything they say it is, it could be the answer.

The 950 is so big it's very hard not to scratch the equipment rack when I shift it around to change connections, it has no headphone jack, and it's so tall that I have *just* enough room to slide the Cambridge 640p on top of it.

Suggestions? Some things I'm thinking of are the Parasound ZPre v2, Antique Sound Labs Wave Line-One, the new Parasound Classic 2100, and the Shanling HP3000 tube headphone amp, which has 2 switchable inputs and an R-L pair of RCA outputs.

Although I'd like remote and headphone jack, if the sound is enough better for the money, I'll sacrifice features for a higher level of musical involvement. I want the one that most compels me to listen.
Try Sonic Euphoria PLC, passive line stage. I think there is one for sale in your price range. I tried it some time ago and was pleased with its involving / engaging nature. Possibly because it was so quiet and neutral. However, my system then was rather complex. I've since greatly simplified and gone with an "integrated" control amp that has surpassed my expectations.
I can see where a passive pre would work well between a CD player and a power amp; would it work as well following a phono stage? The 640p only puts out 300 mV.

There are some fantastic integrateds out there. Which one did you get? I wouldn't mind a Denon PMA 2000, but it's just too big (19" deep) and too hot for my rack space. I also have read so much good about the Onkyo class D A9555 integrated; it seems just about perfect except it has no pre-outs and I'm bi-amping.

But thanks a lot for that recommendation. After checking around, I see that you've given me a way to get about $3K of performance for about $650.
I have owned many passives, most recently Placette, Goldpoint, and BENT-TAP. For bang for your buck, and possibly in absolute terms, impossible to beat he Music Reference Pot-in-a-Box for $135 using a old Noble port used in the original ARC SP-6. It would not work with your phono without a step-up device. But on CD you would be hard pressed to find better sound assuming you have 100kohm input impedance on the amp - typically a tube amp.
My integrated is PS Audio GCC-500 times 2! Check it out in my system.