Hi Shaun,
Far be it for me to disagree with Carl who may have heard a G61R against an 861V4 and since I have never heard a G61R I can't make that comparison.
All I do know is that my DSP5000 24/96 setup saw a marked improvement in sound depth when I moved from an 861V2 to an 861V4 and the guy who purchased my 861V2 reported a jaw-dropingly better sound improvement over his 581.
/Marcus

Lounge: 861v4+ID40 (hardwired Cat 6), HD621, 2xDSP6000.2VC (l/r), DSP5500.2HC, 2*Jamo ARTina (rears), D2500, 556, 596P, PS3, Humax HDR-1000S
Bed 2: MD600 (hardwired Cat 6) , QNAP 453 Pro