What should I upgrade first amp or preamp?

I agree with Ejlif. A new preamp would be a better choice over a new amp. Looking at your system, though, I think your weakest component is the Oppo. Both your amp and preamp are 0 feedback, fully balanced designs. Take advantage of those features by getting a source that is a better match for them. The first player that comes to mind is an Ayre C5. It should play all the audio formats your Oppo does and is a much better match to your current system. There are other good players, as well, but that would be my 1st choice.

I agree with Zd. Another option would be to send your Oppo to ModWright. I think you will be very pleased with what comes back.

Thank you for your responds. I looked at ModWrite ipgrades befoere, however I'm not a big fan of tubes and prefer SS in all chains.

Why not upgrade power cords and add power conditioner which will be far cheaper than adding new component.

Most high end equipment has the potential of performing much better than what most audiophiles are getting out of their systems. I have done quite a number of experiments over the years using a range of cables, conditioning, tweaks etc. I have been amazed at the capabilities of even fairly low priced gear when the right supporting elements are in place. Sometimes it takes some patience, but in most cases major improvements can be made at very reasonable cost. I agree with Lapierre that keeping what you have and maximizing performance is the most cost effective way of making upgrades. As a starting point you might want to check the Mapleshade web site.