The Citation four channel 5.1 100x4 and 7.1 150x4 amps (designed, made, serviced side-by-side Proceed amps) are great too, hugely discounted (selling for less the 1/3 of original $1850 and $2800 retail prices), with under-rated power. Use 3 channels for the 2.5i & AC1, and the 4th to drive a passive sub (ie, NHT 10inch SW2P, 12inch SW3P, or an SVS).