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.