I use a Placette Passive with excellent results. It has 3 inputs and two outputs. You might want to consider it.
I'm not the seller, but I saw this ad.
Depending on your budget and your preference for a resistor-based or transformer-based passive you may want to consider:
Space Tech Labs
All of the above will let you have as many inputs and outputs that you require. I just recently went through this process and in addition to those above, looked into the Placette, Reference Line, Luminous, and Bent Audio. In the end I decided to have a TVC built for me by Kevin Carter at K&K Audio that uses S&B transformers. This will run higher in cost than those you listed and some of those I mentioned, but Kevin's work is great.
I have the Adcom 750 and I like it. It is a Nelson Pass MOSFET design and is a Stereophile Class A rated pre. Since you have an Adcom already you might get a little since of Synergy using them together. I've seen them here and on Ebay going for 750 used. I don't know how many outs it has though and it does not have a phono stage either. It can be switched to passive mode by flipping a toggle switch. Read the reviews on this piece of equipment.
Without doubt, forget the others there is only one passive!
The music first Magnetic passive pre. I have owned this baby for 2 years and it still amazes me. Every up grade I make is in the correct direction from now on.
It slaughters all competitors for many reasons; firstly it is built by Stevens & billington and uses transformers. Do not bother with resistive passives as these types are of no use except to show us the way to true purity of sound.
The music first is not only RCA but is balanced and this is where passives take on a new meaning. If your power amps are not balanced then buy it as it will operate in RCA but when you get a balanced power amp you will not believe the silence!
The silence and power! You will not doubt this passive! You may doubt the rest of your HiFi but not this baby.
The journey is just begining