I am currently in process of doing something similar to what your asking. TimberTech Radiance Rail with IPE as a top rail. I'm trying to determine what would be the best way to connect the IPE to the rest of the railing, the only contact the top rail makes is the posts. I'm thinking of just screwing down the top rail into the 4x4 PT posts and plugging. What were you thinking of doing? P.S. I'm using a 5 3/8 IPE railcap and found that when you set the railcap over the radiance rail post slips, it doesn't completely cover them - you have approx 1/16-1/8 of the post slip edge showing (on either side). The overall width of rail cap is actually wider then the post slip, but the profile of the rail cap cuts in making the bottom side a little just a little too narrow to completely cover the rail. I can take a picture and show you if you don't already have the prdocut to test with.

Home inspectors when I've sold houses before, note when things are not to code and with our previous minor issues (like a hand rail being too thin?), they don't prevent the sale of the house, they just alert the buyer. Anyways, not concerned about this specific picture's accordance to code, just looking for the cost estimate. Palimpsest - thanks! That's what I was estimating in my head, great to know!!!

Be sure to sell or give away that beautiful old railing and not throw it on a heap. I happen to like it. But indeed, it might look better in black. The railing you have posted instead gave me some shudders. Quite a contrary style and not one I'd welcome in my home. Way too modern for a ranch home, is what comes to my mind. If you are really going to get a new railing, I like the one Judy proposed, although I wouldn't want it in white at your place. Perhaps in black and the railing that matches the wood of the stairs? Or maybe something like this?

you need to work with a pro who has a little creativity because your objections really shouldn't be a big deal. To keep the p/t lumber from being visible, use a stainless steel grommet in the ipe post trim with a hole bigger than the one holding the cable in the p/t post. for the cap rail, do a metal cap rail to meet code, then router a channel in the ipe and mount it to that. Done. It'll take a little bit of design time to ensure that all your proportions are right and everything ties together appropriately and structurally, but there are definitely ways to get the look you want while satisfying the permit store. Obviously not dimensionally accurate or really thought through in terms of attachments, but here's the gist.