Hi DES has two modes ECB mode (Electronic CodeBook)and CBC mode (Cipher Block Chaining) IPSEC uses CBC mode but CBC mode is used by 3DES and also 3DES
Because non-cisco firewall offers DES-CBC I suppose that is simple DES (not 3DES) so you should have esp-des on ASA too...
Try if is possible to set non-cisco to 3DES-CBC it should be more secure than simple DES
M.
Hope that helps, rate if it does