Upgrade amp power cable or not?

If it was me I would upgrade the Monster conditioners first, before getting a new cord for the amps (which is also worth it). What is your budget? For a low cost conditioner consider Chang Lightspeed, Tice, or Audio Power. Preferrably one with an IEC, so you can upgrade that power cord as well.

Actually I have owned four Monster Conditioners. It is OK for connecting a receiver, VCR, and basic TV (which is where my remaining ones are), but it is still a cheap piece of plastic. Just remember the reverse. Many of those that don't believe in a good power conditioner, don't own one, and therefore have not or cannot compare a cheap conditioner with a good one, and with just plugging into the wall.

Some are blessed with a good clean power source, and some higher cost gear actually has a built-up power supply with some conditioning techniques built in. I'll hear from some that say conditioning does not work, and they list their gear which includes components with their own built in conditioning. So it does work and they don't know it.

I know from years of testing in my home the value of a good conditioner, good cables, and clean electric power. They all have their place. Unless you have dedicated lines, plugging into the wall is in many cases not the best answer, especially for those in apartments.

The better conditioners are not filters that restrict power. They operate parallel to the circuit, so the power still flows.

Audio Prism makes a device called the "Noise Sniffer" that basically "plays" the noise in your lines though a speaker on the unit, so you can hear any noise.