Re: A3 in a Seth ?
Thames,
I would go with the A3 first, and see if it does the trick. The A5 might make it too bright. The great thing that the Seth has going for it (aside from being a tonally phenomenal pup) is that it retains it's mids. This will help balance the increased highs of the A3,4, or 5 magnets.
Good luck,
Jeff