Digital BW, The Print

Hi Dan,
first of all, it's worth reading a couple of books - Real World Image Sharpening my help you, as may Amadou Diallo's Mastering Digital BW Printing.

Second, when I'm enlarging from my low res DSLR, I add some grain digitally to avoid the 'digital' look and make it look more like Tri-X - the grain gives the eye something sharp to settle on and removes that artificially smooth look one can get from enlarged digital files. 

If, like me, you are stuck with limited equipment, you have to find a way to harness its limitations, so you can get an aesthetic from it which works for you.

Stitching is another solution that was mentioned. I was shooting for 16" square prints from my D70 ... from stitched mosaics of a minimum of twelve frames to give a 5,000 x 5,000 px image (often extra bracketed frames were stacked for extended dynamic range). My gallery manager thought I'd used a Hasselblad.

Since then I went back to film and a Rolleicord - because I could get all the information in one exposure.

Good luck,
Richard 
Richard Smallfield Photography
http://richardsmallfield.com