According to the 'option board applicable list' (
http://accuphase.com/cat/option_board.pdf)
you can use any board from AD-290 to AD-2850 with your C-2400.
According to 'product museum' (
Accuphase Laboratory, Inc.?Product museum)
AD-290 is from 1993.11
AD-290V is from 1998.12
AD-2800 is from 2002.07
AD-2810 is from 2008.01
AD-2820 is from 2011.12
AD 2850 is the current model
Likewise the separate phono preamplifier
C-27 is from 2008.12
C-37 is the current model
Does anyone really think, that Accuphase did not (significantly) improve their phono stages over all these years?
The development continuously went towards more neutrality, which means that the sonic properties of the cartridge were increasingly better revealed (similar to the higher transparency of the preamps themselves). Therefore you need to choose the right cartridge for you.
Generally I'd suggest you go for the current models (AD-2850 / C-37) or for the latest you can afford.
Martin
SME 20/3, SME V, AQ WEL Signature tonearm cable, AC-5, C-37