I agree that an original Becker with mp3 added is the best and most original solution, but it also presents the challenge of first finding a functional unit in the first place (after all we're talking about electronics that are older than a lot of us), have the mp3-input added etc.
I have a closet full of Becker radios in my queue for some sort of refurbishment, mostly cleaning and testing. Here is what I have learned about old Beckkers:
1. More often than not, an old AM/FM Becker works right out of the junkyard. I have sprayed the insides with tuner cleaner and gotten very good sound out of most that I have tested. The most common problems are cosmetic (faceplate cracked, knobs missing, chrome pitted) or that the clutch for the tuning knob needs to be adjusted so that it moves the needle.
2. More often than not, Beckers with auto-tune (wonderbar, seek) will not work correctly. The radio will work correctly, but the wonderbar will either work only in one direction, not at all, or ....
3. More often than not, the amplifier for Becker's with separate amplifiers work correctly.
4. More often than not, Mexico cassette decks don't play cassettes well. (rebuild kits are available, but who owns a cassette anyway).
5. Older Becker Tube radios or hybrid radios present a LOT more difficulties in getting them to work well.
My first choice for an old becker (assuming you have a large-face opening in your Pagoda) would be a Grand Prix because you get the push buttons, a separate amp, and maybe even the wonderbar. My opinion is that the Beckers with the separate amp sound better than the ones that are all-internal. Realistically, a stereo Europa would be a great choice and should not cost all that much. My last choice would be a tie between the 6-button Europa (buttons too small) and the Mexico (no preset buttons).
Regarding mp3, Becker radios with separate amps all have a plastic plug in back. You remove the plug and replace with an adaptor plug that has a 1/8" jack in a little box on the end of it and it becomes a switched MP3 input. I think that the sl113 technical manual actually has the wiring instructions for the adaptor. This may also be the case for Beckers that do not have a separate amplifier -- I can't remember at this point.
Finding a Becker pinstripe that works is not that much of a challenge.
<15 minutes later>
OK, so I was overly optomistic regarding ebay. It seems that prices are higher and there aren't many. This only means that I should get busy and clean up some radios and list them!!!!!
Anyway, I still vote for a pinstripe w/ MP3 added.