sports cats for 3.0Q?

[fourcircle]

a few years ago my car was suffering from the common cat problems that often come along with the 3.0 quattro. Instead of paying crazy money to buy new dealer cats (one for each side. each unit comprises the downpipe, small pre-cat and main cat) I bought a Milltek cat back system (from an S4 since it's the same for a 3.0Q) and had someone local gut the pre-cats, cut out the main cats and weld in two S8 cats that I was given. All was reasonably well for the past 3ish years like this, apart from one of the rear lambda sensors dying almost yearly. A few days ago I noticed a rattling and after getting under the car I realise that one of the main cats has partially collapsed inside. The EML has been on and off for about 3 months but I haven't paid it too much attention and kept thinking I'll change it soon when I get a moment (It's been a busy year so far). As far as I'm aware it only tells the ECU whether the pre-cat on that side is working. But maybe it has been causing over fuelling, which has wrecked the cat. or maybe it's something completely different?

So now I'm thinking about my options. Milltek don't do downpipes for the 3.0Q. I can't spend crazy money at the dealers. So I should probably buy two high-flow sports cats, cut out the old main cats and have the sports cats welded in. Maybe I should use the Milltek non-resonated pipes I have spare in my garage and ask a local exhaust specialist to use them to make new downpipes at the same time?

Does anyone have any thoughts on this or even where to get decent sports cats?
Cheers
Nj