Fat Dots are highly efficient. Extra-Thick Dots with Ascendo Special wouldn't be overkill, but more than you need. A fifth Dot under the middle of a speaker cabinet always has potential for additional benefit; I would suggest the Von Schweikert Special for the moderate-weight C8 speakers.
Either five Iso-Cups w/SuperSonic Hardballs or five Extra-Firm Tenderfoot isolation feet should do very well with the amp. Four is usually sufficient, but with an amp that has a fifth support, there's usually a benefit there. With amps having a fairly large base or "footprint," a fifth footer is usually beneficial, anyway. With free-standing Iso-Cups or Tenderfeet, you have lots of latitude regarding placement of the footers, so can usually find optimal locations for the footers--usually, just placing them where they seem right achieves more than satisfactory results, though some experimenting/auditioning with placement can sometimes be rewarding. Neither Iso-Cups nor Extra-Firm Tenderfeet have inherent advantage over the other--either should do very well; subtle comparative differences between them sonically will vary from one system to another, depending on vibrational environment and overall system variables and synergies.
Herbie's Audio Lab