Bret,
You can't lump all SDRs into one category where audio is concerned. Thetis is totally unique in its capabilities. No other radio, SDR or otherwise, comes anywhere close to Thetis in terms of audio processing capability, not Flex, not Expert (Sun), nobody. With Thetis you thousands of dollars of audio processing built-in for free!
But for other radios external audio processing gear makes total sense. For radios where external audio processing gear is desirable, you can do a lot better than W2IHY for the same money. Used professional gear will provide a lot more capability and quality for the same investment. dbx, the brand that Rob favors, is an excellent case in point. If you look on eBay, the combination of a used 286 mic preamp, 166 dynamics processor, and 131 EQ will cost you under $300 and is so much more sophisticated than the W2IHY gear. The only downside is you will have to make your own cable to the radio, which really isn't that big of a deal.
The other thing to consider is that you have fallen for the PR40 trap. The PR40, and other mic's like it (and anything from Heil), is designed to do a lot of EQ
in the microphone. So if your voice is not a good match for the mic you wind up fighting the mic with the EQ, which is just dumb. It made sense back in the day when EQ's were expensive and/or not built into every radio, but it doesn't make sense anymore. My advice is to buy a mic with the flattest, most uncolored response you can get, something that will transduce your voice honestly without any changes. Then add EQ to that as desired. Mic's in that category include a long list of large diameter condenser microphones including the Behringer B1, MXL550, Audio Technical AT2020, and several others. These mic's do require 48V phantom power, but you can buy
48V phantom power supplies off of Amazon for $20 or $30. Or, if you decide to use something like the dbx 286 it will be built into that.
73,
Scott