We use the IRS Address. Until the last release, this was problematic however, because IRS Address only had one line (no City ST Zip fields). That is better this year, however the biggest problem remains, you can't see IRS Address on any inquiry screen. We're voting for it in the next release.
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"No problem can withstand the assault of sustained thinking." ~ Voltaire
"Sustained thinking gives me a headache." ~Me