IO Signature/Steelhead/Arc Reference/ and Colibrì?

I would go for 4 & 1, because:

*I like the Io & the Steelhead riaa's, obviously. I liked these better than the ARC. Of course, all are exquisite sounding.
*I like to drive the amp directly, and don't feel the need for the extra db the line part will give (my amps have over 47kOhm input impedance -- so a sort of OK load).
*If I felt the need for extra amplification (a line), I would stick with either Aesthetix or Manley -- probably the latter (there's slightly less tube maintenance required and I'm getting older & poorer)

The Wavac phono could also be considered (with passive riaa equalisation & transformer coupled attenuators). It's astronomically priced, as you can imagine...
I dared listen to one recently (I mean, it was free to listen to... you never know at these prices:)). Well, superlatives don't serve anymore, and since I will never be able to buy such a product, I thought I'd just mention it for academic reasons...

I have a great deal of experience with all of the pieces you mention. I am also a dealer for a few. The Colibri is my favorite cartridge...fantastic!

My favorite on your list would be the Manley Steelhead for a number of reasons.

1. On-the-fly adjustments for extreme flexibility.

2. Great customer service and loyalty from one of the best audio companies around.

3. Extremely solid and reliable product.

4. Tubes that are easy to roll for tailoring to a particular sound.

5. Ability to run without an additional linestage.

6. Solid bass and phenominal detail with a very linear sound.

I've used my VDH black beauty ( 0.5 mV at 500 Ohm) with ARC SP-11 MKII, counterpoint SA-5000, Marantz 7C with counterpoint SA-2 active step up, HK Citation I with Music Reference RM-4 step up. All sound different. Not sure what you're looking to get out of the Colibri. You need an extremely quiet and black background phono playback for the VDH cartridge.
The ARC SP-11 was a bit underpower for my setup but it sounds big but lack of punch. The Counterpoint is nice and sweet with slower rhythum. Smaller, and more conerntrated mid range. One of the most articulate vocal you'll ever hear. The Marantz 7C is nice and warm but lack of fullness of the Counterpoint SA-5000 and lack of cleaness of the ARC SP-11. When combined with Counterpoint head amp, it is a bit softer but not as sweet tone. Sound stage is slightly bigger than counterpoint SA-5000. The HK Citation I is also one of the great vintage preamp for MM. Using it with Music reference RM-4 head amp, the unit is very close to ARC sound with more authority. smoother and warmer sounding than SP-11 MKII.

Aside from my own setup (with my limited budget), I prefer 2,3 and 5 choices. The line stage is quite important too. It helps balance the signal before it gets to the amplifier stage. Ineed a bad line stage can introduce color into the sound.

Zender, you haven't described the rest of your system or your tastes so everything I say will have to be taken in context. First, I have to say that as a former owner of three different Colibris, I know it's sound and strengths fairly well. When properly set-up and mated, it can be devastatingly fast, detailed and can lay it all out there for you to hear. However, in MY experience, it can also sound sibilant, a bit thin and tilted up if everything else in the chain is not either set up properly or compatible with or complimentary of the Colibri's strengths.

Next, I have owned the the Lamm LP2, the original Io, the Io Signature (both with and without dual power supplies) and the latest Manley Steelhead.

From the standpoint of easy adjustability, obviously the Manley is the best option. Personally, I much prefer the Io Signature for a couple of reasons -- for MY tastes, the Io Sig has a bigger presentation, better dynamics, increased separation of instruments and voices and a better ease of presentation (effortlessness, if you will). I am not saying the Manley is a slouch, but for me and 4 of my analog buddies, we all agreed, the Io Sig brought new life to my analog rig. My comparisons are based on STOCK tubes in both.

I must also admit that I did NOT tube roll with the Manley (which I understand can improve it noticably per my friends) and that I NOW have tube rolled with my Io and it can truly be tailored to suit your needs with tube changes. Tube rolling will be more costly with the Io as you know, so if funds or hassling with many tubes ain't yer cuppa tea, again the Manley is the better choice. Tube rolling can also make the Io MUCH quieter (which has been a knock against it vis a vis the Manley by some).

Next, if you are NOT doing analog, I wouldn't bother even considering a line stage and the attendant cost (e.g., not just the line stage but the additional power cord and interconnect) or placing another component in the chain. So, if you are JUST doing analog, go with the Io or Manley with volume controls (I am NOT saying that some do not prefer running the phono stage through a good line stage). I use a line stage for my digital and phono so I do not need the volume control.

On the issue of reliability, I previously reviewed the original Io for Ultimate Audio Magazine way back in 2000. At that time, after my review, I and some of my friends experienced some problems with our Ios. Jim White always fixed them quickly and without charge but I was losing faith in the unit. Since then, I learend that there were defective Mills resistors in the units (in fact, I was informed that Jim White won a lawsuit against Mills) and Jim has replaced or offered to replace all Mills resistors in existing units (with Roedersteins) for free. Since I got my Io Signature, it has been totally problem free and Jim White is a pleasure to deal with and his customer service is great!

Finally, the Io has easily adjustible gain (even without the volume controls) and loading.

In this league of phono stages, it really comes down to personal preferences. Since I like the lifelike presentation and since I value effortlessness and great macro and microdynamics, I sold my Manley for the Io Sig. But, as always, your mileage may vary (particularly if your table/arm and system synergy dictate otherwise).

I hope this helps