First off gentlemen Jack is a master printer and this is not kindergarden teaching. Second David labs uses a Lightjet which has it's own hardware interpolation built into it , so he does not have to do anything to the file the hardware and software does it. Not the case with Epson inkjets.
Lightjet
4. Real-time Hardware Interpolation
Using our proprietary adaptive 16-point bi-cubic algorithm, the LightJet enhances sharpness through on-the-fly pixel interpolation. Because the pixels are faithful to the original image, the system can output small files at high resolution with no loss of sharpness. Unlike software interpolators which limit the flexibility of the interpolation process, our hardware uses complex algorithms to produce the best possible results. For example, the LightJets adaptive interpolation gives users the ability to sharpen some areas of an image, while maintaining softness in other areas - no other printer has this capability.
5. High Productivity
With the 200 dpi option, the LightJet will print a 50x50" image in 4.1 minutes (on RA4 paper). Smaller prints are produced even faster. Inkjet printers operating in "photographic mode" can take up to 10 times longer to produce a half-tone image.
6. Optional Software Optimizes Workflow
Cymbolic Sciences has created an open interface that allows for numerous workflow solutions. System Manager XL is optional software that incorporates invaluable features that can accelerate workflow when producing a mixture of print sizes from a variety of image data files.
The software accepts PostScript (RGB/CMYK) and TIFF (RGB/CMYK) intermixed on the same page with no preprocessing required.
The integrated PostScript RIP automatically calculates and RIPs file to size with no operator intervention
Both PostScript and TIFF files, either in RGB or CMYK, can be previewed and color adjusted. Visual feedback is provided to the operator for color correction.
CMYK files are converted to RGB as the files are imaged with no pre-processing required
Different color corrections can be applied to individual image files that are printed on the same page
Distinct sizing, cropping and interpolation factors can be applied to each image on the fly while imaging.
Let's not confuse commercial laser printers like a Lambda and Lightjet to inkjet printers there different beasts altogether.
More info on Lightjet
http://www.cymbolic.com/products/lightjet5000.html