Candidly, what you describe makes no sense to me. I will assume the probe flue thermometer reads as you say, 500-600F; and that wood truly is about 20% MC. Next I assume you have relatively small splits, no larger than 5" and many smaller.
The Solo 40 (at least mine does) has a viewing glass into the gasification chamber. With the secondary air lever set in the middle (forget about any other adjustment), the viewing glass should show blasting orange-blue-colorless flame into the tunnel and blasting out towards the viewing glass. And I mean blasting. Feel free to open the lower door to take a better look once in awhile, if you want. It should look and sound like you think a blast furnace might look and sound like (although I don't know what a blast furnace looks or sounds like). You shouldn't have any dripping creosote in the upper firebox, but a coating of creosote with some flaking along the top and sides, quite thin, and mostly stuck hard to the metal, is usual. No drips down the sides onto the refractory. And nothing should be blocking the gasification slot into the tunnel below.
If all of this is happening, operation sounds normal to me. Wispy steam, and even occasional smoke, all is usual, especially in cold weather. Smoke will occur occasionally based on burning conditions in the firebox, but it usually will correct itself (or poking down the wood burn load a little also helps, but don't block the gasification slot). Small splits really help to eliminate any smoking.
I assume in the past you haven't creosoted up the firebox by burning bad wood, and that creosote hasn't dripped into your airways. The manual mentions the rare possibility of this happening. If so, you've got to find a way to clean out the airways. Call Bioheat for help.
If all above is OK and you truly are getting smoke (if smoke, you should be able to really smell smoke outside), then I would take a look at where the damper is set on the draft fan. It has two adjustments, a fine adjustment and a basic adjustment. Start with both set so that the damper opens 100% with the fan running. This will produce maximum air, and it may be too much. You can tell by the temp reading higher on the flue probe being higher than it should be. IMO 600F with truly dry wood, and maybe somewhat higher, and without turbulators is probably fairly normal. If you have turbulators, temps should drop about 100F.
Last, if temps are above what they should be, you can gradually close down the draft fan damper to reduce the forced draft until you find a satisfactory flue temp and gasification continues normally. If it's closed too much, you may get inconsistent gasification.
I'm not saying you don't have chimney draft problems caused by improper chimney installation, not the right height, obstructions, trees, wind conditions, etc.; I am saying that if gasification is what it should be, there will no or very little smoke, but there may be steam. Steam will be odorless, and if you have a lot, your wood is not as dry as you think.
Hope you solve your problem.
