How to combine multiple repositories?

[Tomas Hoger <thoger@pobox.sk>]

Hi

I'm trying to combine several package repositories, some of them are marked
as stable, some as unstable.  All those repositories contains various
versions of some packages.  I use origin tag from Release file to pin
priorities to packages from this repositories.  Here is snippet from my
/etc/apt/preferences file:

Package: *
Pin: release o=originA,a=unstable
Pin-Priority: 800

Package: *
Pin: release o=originB,a=unstable
Pin-Priority: 700

Problem occurs when I want to install package from originA and originB has
that package in newer version.  I do use

  apt-get install packagename/unstable

since that system is stable with few packages from unstable.  But apt
always tries to install package version from originB, even if it has lower
priority (according to apt_preferences(5), it should not do that).  Is
there any way to tell apt, which version it should install?  Or did I mess
those priorities?  Docs only describe simple repository combinations (like
stable + testing or testing + unstable).

Anyway, those many repositories seems to confuse apt-show-versions too (or
I don't understand how is should work ;).

  apt-show-versions -p packagename -a

prints only currently installed version, the newest version in stable and
the newest version in unstable, even if there are at least 4 different
version of that package in various repositories listed in sources.list.

Btw: Experiments with APT::Default-Release and setting priorities to values
over 990 was unsuccessful ;(.

Is there any way how to make it work as I expect it?  Any ideas
appreciated...

-th.

PS: Please, CC your reply to my email address (thoger-at-pobox-dot-sk).
Thanks.