Okay, I think I have the abc thing licked. Sibelius can export as MIDI and when I then import the MIDI files into a program I found here it spits out something that looks suspiciously like an abc file.

X: 1
T:
N: Instrument Channel 1 ... [Violin]
M: 3/2
L: 1/8
Q:1/4=200
K:F
%Ratclift Cross
%Walsh's 3rd Book of Jiggs etc c1730
%Copyright \0xa9
V:1
%%MIDI program 1 40
%Violin
f2c4 BcA2F2|d2B dGB DGE2C2|EGB AGF EDC2c2|AFE FCF EGF4|
f2c4 BcA2F2|d2B dGB DGE2C2|EGB AGF EDC2c2|AFE FCF EGF4|
cfa fba gfe2c2|Bdg dgf edc2B2|Acf cfe dcB2c2|AFE FCF EGF4|
cfa fba gfe2c2|Bdg dgf edc2B2|Acf cfe dcB2c2|AFE FCF EGF4|
f2c2_eg f_ed BAB|g2d2fa gf=e cBc|a2e2fa gfe dcB|AFE FCF EGF4|
f2c2_eg f_ed BAB|g2d2fa gf=e cBc|a2e2fa gfe dcB|AFE FCF EGF4|
afc fAc fad2B2|bgd gBd gbe2c2|dBG BDG BdE2c2|AFE FCF EGF4|
afc fAc fad2B2|bgd gBd gbe2c2|dBG BDG BdE2c2|AFE FCF EGF4|

Can anyone out there who reads abc tell me if this works?

Cheers

Chris