Catholics believe that during the Eucharist the bread and wine becomes the actual Body and Blood, Soul and Divinity, of Christ.
Most Episcopalians do not believe that. The very High Church Piskies do (I was one before I became a Catholic), but then you have the additional problem of the invalidity of Anglican orders due to the change in the consecration of bishops under Edward VI. No Apostolic Succession, no valid Eucharist.
So a Catholic receiving in another denomination would be acting a lie, so to speak, because you're acting as though it makes no difference -- when it does.
That's also why non-Catholics don't receive in the Catholic church, because they don't believe what Catholics believe and, again, it's acting a lie.
I’m not going to argue apostolic succession. Most Episcopalians I know do believe in transubstantiation. I’ve been on both sides of this issue and heard all the arguments of man but God hasn’t changed. And that’s what is truly important.