There are a few ways to determine the 861 version.

Software Version / Serial Number

If you have access to the processor and can connect it to power you can press the "Display" button while it is in standby. The display will cycle through different pages of information that includes the version number and serial number. The serial number might provide some information although not conclusive since serial numbers are not changed when upgrading the electronics.

Chassis / Cards

If you only have access to photos it can be a little trickier because you can have an old chassis (round gold buttons behind front panel ) that has upgraded electronics. The input and output cards are a little more reliable than the actual chassis but are not definitive since the input cards are shared across a few versions. The digital input card for v1 and v2 is the IE16 and has two fiber optic inputs. The v3 and v4 will have the IE42 and has multichannel digital inputs. The v6 and v8 will have the IE44 and has multichannel digital inputs as well as MMHR and SpeakerLink (looks like a RJ45 ethernet port).

If you share a list of the cards we can help you narrow it down for you.

Nick

558.2 amp, Meridian A500 speakers, M2500 sub, Director & Explorer DACs