Hi, Thank you so much for your advice. Now I have used my system for one month, and I do have some clue about it.
I only use my system to listen to music.
I made my decision to choose this amp based on AudioScienceReview's review. (By the way, they are criticizing RP-600M's crossover hard)
The Echo Link Amp is the cheapest power amp with 80+ SINAD.
And I do think WhatHiFi gives a good review. The Bluetooth is bad sound and annoying to use. The amp (via Bluetooth) also has a lag issue and intermittently stop and go. I won't recommend it to anyone who wants a 'smart speaker amp', the SONOS should be way better.
However, if and only if, when I using my Topping E30 to feed the amp, it does sound amazingly well. I would say, it's beyond my perception. Especially considering the cost ($209.99 on Prime-day).
Because I got my RP-600M from eBay and only cost me $2XX/pair. So I've also limited my amp budget.
This is just my first pair of speaker, I don't want to spend too much money until I have a more clear idea about what I want.
And my thought on the next step will be.
0. Make up my mind to buy a pair of stands. I couldn't understand how the stands are so expensive. (Now using 'Bookshelf')
1. Get an SVS sub. Probably the SB-2000.
I've tried a Klipsch R12SW, Costco has them on sale for $149. Sounds good. But not deep enough. Yes, I'm talking about 'Bass I love you'. Normal music doesn't need an infrasonic response, but SVS advertising is so addictive.
2. Get another Echo Link Amp (Or something better like Schiit.), and Bi-Amp/Active-Crossing my RP-600M with miniDSP.
3. Begin my audiophile life and dump money into it. Planning to get the Genelec SAM system. However, I don't think I really can tell the difference. The Klipsch really sounds AMAZING!