A few points occur.
I assume you are using the D-75 at stock strength? If so, for the Delta films change to 1+1 which is generally considered better for Delta and Tmax emulsions - dilute the stock developer with the same amount of plain water. Use the times given in the Ilford data sheets for 1+1 dilution.
Use Ilford's agitation style (ignore all shop assistants until you know them well enough to know if they know what they are talking about). Ilford times = Ilford agitation: they are directly related. Pour the developer in, immediately agitate for 10 seconds then for ten seconds every minute. Agitate by inverting the tank and then righting it again - do this 4 or 5 times during the ten seconds.
To get more shadow detail, rate the film at a lower ASA. Start by reducing by 1/2 to 2/3rds of a stop (whichever is easier for your camera). Still not enough shadow detail - reduce further. If you end up at much over half the original ASA (Delta 100 below 50ASA or HP5 below 200ASA) you have probably got other problems...
Once you have the shadow detail you want but the negative is too low in contrast, increase development time by 15% (but watch out for Delta - the newer technology emulsions are more responsive to development time change so try 10% there).
The other slight problem is that all the B&W people here (99.9% anyway) use a traditional darkroom and only a few scan for a final print and digital subjects are off topic here, so it's all a bit difficult...
Have a look at APUG's sister site
www.HybridPhoto.com which was set up specifically to discuss activity where film is only a part of the process. People will be able to discuss the scanning side more freely there.
Good luck, Bob.