The Cup Of Kiddush

Tosfos in the beginning of Arvei Pesachim explains that one has to wait until nightfall to eat the matzah since regarding the korban pesach it says it must be eaten בלילה הזה and mazah is equated to pesach via a hekesh.  What about the kiddush ,the first cup of wine, does that have to be done only after nightfall?  The Taz (472:1) says that since matzah must be eaten after nightfall so too kiddush since kiddush must be done at a time when one is able to eat the סעודה.  The Magen Avraham says since kiddush is the first of the four cups of wine and the four cups of wine are connected to matzah.  It is unclear in the words of the M.A. why are the 4 cups connected to matzah?  The Alter Rebbe adds that the 4 cups are Rabbinic and the takkanah follows after the din Torah of matzah.  In other words, the Taz uses a technical law in kiddush to say the kiddush must be connected to the seudah so it must be done at night while the Magen Avraham says intrinsically the four cups are connected to the matzah.  (This is how the Mishna Berura seems to explain it as two distinct sevarot but the Alter Rebbe uses also the words of the Taz in his explanation, and he may have understood they are saying the same thing.)  Why do they give two different explanations?  

The first cup of wine is both the first cup of wine and the cup of kiddush.  The M.A. views the kiddush itself as subjugated to the rules of the four cups while the Taz is of the opinion that even though the four cups may be connected to the Haggadah, the kiddush itself in theory could have been said earlier if not for kiddush במקום סעודה.  

The Tur (483) cites a machlokes Rishonim if one who does not have wine says kiddush on bread like any other Shabbos or Yom Tov or since there is a takkanah of 4 cups, one may not say kiddush on bread at all.  This would seem to parallel the same issue, if kiddush is kiddush just it also happens to be one of the 4 cups, one can say kiddush even without wine if necessary.  On the other hand, if one is of the opinion that the kiddush of Pesach night becomes incorporated only within the rubric and rules of the 4 cups, one would not be able to say kiddush on bread (see sicha second night of Pesach 5725, עיונים בלומדות כלל ה.)