Digital BW, The Print

I am currently scanning some of my B/W negatives (Tri-X) using a 
Minolta 5400 and VueScan.  Fine tuning is carried out in PhotoShop 7.

My workflow is:
Scan the negative as a 48bit (RGB/tiff) scan.  In PhotoShop covert it 
to a Greyscale image/adjust the levels/adjust contrast.

This is OK but I find unless I adjust the contrast my images are 
muddy.  I have found that taking the RGB scan/converting to Lab mode 
and just viewing the Lightness Channel is a good way to go BUT if I 
stay in 16 bit mode it does not let me discard the a and b channels.

Is there a way I can do this and stay in 16 bit mode?  How do you do 
it?

Cheers

Martin