I would always use new gaskets for the inlet. mine bent quite badly when it was removed.
Even if they do seal with instant gasket, there is no guarantee they will stay sealed under boost.
it's also a little difficult to re-fit/re-align the inlet what with having to get the turbo hose on etc....
is the DV re-circ connection to the new silicon intake pipe blanked correctly, this will join to a hard cross-over pipe near the turbo.
there are sets on ebay from a jap parts importer and they are genuine subaru.
could be DV but expect it to be an air leak engine side of throttle housing.
DV connects (small hose) to engine side, so try blocking that and also remove DV and bung the hole with a steel cap (or 19mm socket
) for a trial run.