Proceed HPA-2 Quality Issues? Sound? Tube Preamp?

I just bought a HPA-2 in mint condition. It will be to me next week. My question is I saw on some other websites that there are quality issues with Procced product, are there? Is it a keeper? For what I paid ($500)I think it was a steal and at that price should I sit back and enjoy?

Can any body offer opinions on the sound quality and what preamps are you using?

I would like to run a tube preamp with it.