Advice please folks: I have a Denon X4200W running a 7.1 set up. I would like to add two upfiring Atmos speakers to make it effectively 7.1.2, however the amp will require an external amplifier powering the additional speakers via the pre out. Can anybody recommend a good budget priced amp for this purpose? I'm not sure if it is cost effective to find one or sell the 4200 and seek out a 5200. Thanks.