I think that having higher order interpolation opcodes may not really
be necessary in csound.  Here are several reasons:

1.) You can do it if you need it in an orc using phasor and table.  Just
take the two adjacent values and interpolate any way you want between them.
2.) It doesn't make much difference if you use large tables.  Most of us
have lots of RAM and can make our tables as large as we like.  The
interpolation error for a 200 Hz. sine wave using a 16k table is very
very small, and unlikely to be improved by a higher order interpolation.
 The sound card probably has memory restrictions, so they use small,
down-sampled tables and try to make up for it with a higher order
interpolation.  So what you are really seeing in their spec is their
low-cost solution, not a leg up on csound.
-- 
Mike Berry
mikeb@nmol.com
http://www.nmol.com/users/mikeb