I would say hold on to the Portico and get some nicer converters. I would assume that your portico will have a much larger difference in quality after comparing with the better converters. After I got my Benchmark I noticed a lot of stuff I didn't hear before. I could tell very fast what were my cheap mics, and what were the "big boys".
Some great options are the benchmark, UA 2192, Apogee Rosetta 200, Lucids, Myteks, etc. I have not used all of these, this is just rehashing other opinions from the forums

However I can attest to the benchmark, and I am ordering a 2192 on Monday so I will know more about that one next week.
If your budget is lower, then I agree with the Onyx converters, or something like an RME multiface.
Good luck