Hhhm, sometimes one cannot see the wood for the trees. The reason why
"subha-nimitta.m" cannot be translated properly as "pleasurable [sense]
object" is quite simple: there are no pleasurable sense objects. They are
just objects and it is we who make them pleasurable or otherwise. Thus the
experience of pleasurable nimitta.m must be a mental event synthesized from
the raw sense data, vedanaa, memories and conventions etc. If the sense
object itself were pleasurable, then it would remain so for all people,
which is clearly not the case. Take, for example, opera. I know of people
who find opera a highly pleasurable experience, whereas to me it is little
better than a caterwauling cacophany (ie rather unpleasant). But there is
nothing in the combination of operatic sounds per se that is pleasurable or
unpleasurable -- it is one's nimitta (image) of the bare sounds that make it
one thing or another.
This, as Dimitry points out, is more than just a matter of translation
niceties. With a little thought one can see how "pleasurable sense objects"
and "pleasurable perceptual images" would require substantially different
methods of dealing with them in one's practice.