"That is my problem. I "properly" underexposed the K-14 slides and they look great to the eye, but the scanner can't seem to punch through them. I'll work on it some more."
K14 Kodachromes can have a real d-max of up to 3.8 and your scanner only can capture about 2.8 d-max, so it's no wonder you're losing the bottom three or four stops of detail on your scans. The ONLY way to scan Kodachrome is with a sensor that can record all the way down to a 3.8 or higher d-max and that, of course, means a photomultiplier tube and a drum scanner. There simply is no CCD scanner, no matter what the claims, that can scan anything above about a 3.0 d-max, even the much applauded Imacon.
"But maybe I'm more picky now."
Undoubtedly. That's a good thing.
In my experience, outside of contemporary scanners, the mainstay "pro" scanners of several years ago were pretty good, My Umax Powerlook III can reliably scan a dmax of around 3.0 (specced at around 3.8) and the Opal Ultra can do just a tad better. It's important to remember that they were designed to scan comps of E6 product work, typically lit rather flatly (due to repro dynamic range limitations) and detail in the deepest, darkest areas really didn't matter for an FPO comp.
Those limitations not withstanding, I've tried newer, consumer grade scanners and quite frankly, idiosycrasies aside (SCSI interface, size, less than intuitive software), I still get a better image from my older flatbeds than anything newer (at least in my price range). You have to work harder to get it, but the latent capabilities are there if you're willing to optimize your workflow. The transparency adapters need some modifications (such as a fastidious cleaning of the optical chain, matte scotch tape diffusor added to the light source, critical mechanical adjustment of the focal plane, sealing the cal strip so oil can't infiltrate it when wet scanning, etc.) but can get you 95+% of the way there.
for B&W scans, I find Vuescan's multipass and the ability to lock exposure settings invaluable, especially when scanning numerous negatives all shot at the same time and processed similarly. with some scotch tape stops, I can scan lots of 4x5 negatives fairly quickly dry mounted, and then if I find an image that warrants the "full treatment", I can take it and wet mount, multipass scan and get as good an image had I sent it out for a drum scan. Granted, I shoot about 75% B&W, about 20% C41 and only occaisionally venture into E6 land, and primarily Xprocessed at that.
For smaller formats, I find that unless I need something very critically done, I can use my Beseler Dual Mode Slide Duplicator and a Kodak SLR/N and get very good quality scans ( up to 10x15) very quickly. If need be, I have the Frontier at the studio, though this time of year a few blocks walk seems like torture.
