I made&used a deck similar to this one on war#5 support in round 10 vs time & fire, twice.
Here is the time topic. Fire topic got deleted in forum bork. I lost both, however, to my defense in both cases they had creatures above lightning range so i was half-countered and i had beyond terrible skull shield proc. In that deck, I would use arsenic and DS if those cards were allowed.
In your deck, silences would probably have a hard time holding the opponent creatures long enough and they are in fact combo in itself. You need to chain, so you need to draw multiple of them early. Otherwise silences are no use once the opponent sets his creatures on the field so you need protection of shields and/or set of lightnings. This deck is a foreplay for the classic bonebolt with poisons.
If i wanted to build an unupped, generic purpose, stable duo deck involving poison, arsenic and psion, i would build this one:
Hover over cards for details, click for permalink
52o 52o 52o 52o 52o 52o 52q 52q 61o 61o 61o 61o 61o 61o 61o 61o 61o 61o 61o 61o 61t 61t 61t 61t 622 622 625 625 625 625 8pk
However, it depends on the context you are building the deck. PvE ? PvP ? and depends on what you know about your opponent's possible decks. In general, purpose of silences are to prevent opponent's defense or his/her possible OTK. But both poisons and psions are designed to penetrate the defense. So i don't see much point in using those, again, unless you have a special reason to believe you need silence for your match.