Jim,
i have tried both and own an Eden wt800 head. The Metro used only a 12Ax7 preamp tube and a solid state power section.
The Alembic preamps use 12AX7 pre tubes, and then whateverp poweramp you choose to mate it to.
I do not think you can go wrong with either. In fact, I was in the market for both and got the Wt800 because I got a deal on it and the price was significantly lower than the cost of the Alembic pre-amp+power amp schema.
That said, I would still like an Alembic preamp in my rack to have the option because it is a wonderful sounding preamp.
You really cannot go wrong with either.
On the differences, the Eden amp by itself will give you more options in regards to EQing. The Eden EQ is excellent and is very versatile. I would think with -- and correct me if I am wrong -- you may want to add a SF-2 filter to the Alembic system in order to open up more tone possibilities in regards to EQ options. Remember the Alembic tone stack is like an old Fender. You have bass, middle treble, and any adjustment to one affects the other. With the Eden each control is mutally exclusive of the other.
Sometimes, keeping it simple is a much better approach.
It is really hard for me to suggest one or the other. It depends on your needs, size of the system you wish to build etc. If you're buidlign up a big rack system and may wish to add many cabinets to them -- then the Alembic pre + a replaceable poweramp may be the key.
As far as sound goes -- consider guys like Phil Lesh and Roger Waters both used the Alembic F2B throughout the '70s and got some of the best bass tones in the world. Lesh uses an Eden now -- but you have to consider his tone has always been great using either one of the presamps. As well, guys like David Gilmour have made the F2B (modded with an extra 12ax7 tube) a staple of their sound for decades now. And dont forget Sting's tone -- also great -- who currently runs and Alembic F1x as his preamp.
Point is, you cannot go wrong with either and when I have the time/money/etc I plan on having both systems.