in my humble opinion you've got strange advice.
Printer calibration (toner or inkjet) has absolutely nothing to
do with working spaces like sRGB or offset processes like ISO
One prints a so called target which is entirely defined by some-
what round combinations of CMYK values (percentages 0, 10, 20
... 100 each channel).
After drying the print, the CIELab values are measured by a
spectrophotometer, for instance EyeOne Pro, followed by gene-
rating one or more profiles, for instance by GretagMacbeth
The ICC profile consists essentially of multidimensional tables
L a b --> C M Y K and C M Y K --> L a b.
That's all, with one exception: some printers require in advance
to the mentioned process a so called linearization, which can
improve the accuracy, but without enlarging the gamut.
Everything for one ink set, one paper or medium, one type of#
rasterization (different target prints) and many other parameters,
for instance the kind of Gray Component Replacement (GCR)
(different profiles based on the same target print).
Once you've got your ICC profile, you can use documents with
Images in sRGB, aRGB (Adobe RGB), images and vector graphics
in any CMYK space like ISOCoated v2 eci or SWOP.
Source profiles are defined in a Raster Image Processor (RIP)
or in Photoshop. Destination profile is your measured ICC profile
(evtl. plus linearization).
Therefore feel free to use any source profile. Personally I'm using
for Inkjet: aRGB for Images and device CMYK for Text and vector
for Offset: CMYK for everything. The ICC profile as recommended
by the print house. This is assigned to the standard process, even
if the paper should be different.
The conversion from RGB to CMYK should be supervised by soft-
proofing in Photoshop (estimated appearance in CMYK), neces-
sary corrections in RGB.
For gray images, to be printed by K-only, one has to observe the
whole process carefully (preferably delivered as CMYK with void
InDesign handles documents with different colorspaces correctly,
but gray images with gamma other than 2.2 are not shown as
they should be - one reason for not using gray, but CMYK-->000K.
Illustrator cannot carry ingredients with different color spaces simul-
taneously - very bad for general processes.
Best regards --Gernot Hoffmann
P.S.: everything valid for professional toner printers or inkjets,
namely for PostScript printers - not for 'office printers'.
Minor corrections edited by the author
Thankyou very much for your response. What you've said, now you've said it, makes perfect sense.