A couple of weeks ago I bought some Infinity Reference 6.5 inch for my Legacy. When I listen to various speakers in the shop I always like the sound of the Infinity ones the best. Although the 6x9 inch sound a lot better than the 6.5's IMHO (but won't fit in the doors).
The problem you will have, whichever speakers you buy, is making some kind of adapter so they will fit into the SVX door. I can't understand why Subaru don't design their doors to take standard speaker sizes.
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Subaru ECU and TCU Website
1992 Alcyone SVX Version L
1992 Alcyone SVX Version L
1994 Alcyone SVX S40-II
2004 Subaru Legacy 2.5 SE Sports Tourer
1996 Subaru Legacy 2.2 GX Wagon
1988 Subaru Justy J12 SL-II