Here is an example of a printcap file which works with lprps
and an Apple Personal Laserwriter NTR under FreeBSD 6.x:

lp|ps:\
        :br#9600:lp=/dev/cuad0:mx#0:sf:sh:rw:sb:\
        :ms=-icanon,ixon,ixoff,-isig,-echok:\
        :af=/var/log/psacct:lf=/var/log/pslog:sd=/var/spool/output/pslpd:\
        :if=/usr/local/libexec/psif:


And here is a version which works under 
7-CURRENT as of Sun May 20 22:27:18 PDT 2007  

lp|ps:\
        :br#9600:lp=/dev/cuau0:mx#0:sf:sh:rw:sb:\
        :ms=-icanon,ixon,ixoff,-isig,-echok:\
        :af=/var/log/psacct:lf=/var/log/pslog:sd=/var/spool/output/pslpd:\
        :if=/usr/local/libexec/psif:

For sake of comparison here is the sample printcap provided with lprps:

lp|ps:\
        :br#38400:lp=/dev/ttyd0:mx#0:sf:sh:rw:sb:\
        :fc#0177777:fs#003:ms=-isig,igncr,cstopb,-echok:\
        :af=/var/log/psacct:lf=/var/log/pslog:sd=/var/spool/output/pslpd:\
        :if=/usr/local/libexec/psif:

The most significant change is the addition of "ms=-icanon....." 
required by the addition of icanon to the stty defaults in 6.x.
Without it the printer will not show a page. 

For sake of neatness, the (deprecated) fs and fc capabilities 
have been dropped, igncr and cstopb seem unnecessary.

Use of the cua or tty device files seems to work equally well.

Thanks to Per Hedeland for guiding me through the required discoveries.