Could you please give me an advice

Thank you very much for the help and reply above, I will study the manual again. thanks

On many receivers, if you use a left/right analog source, it will NOT process the sound and send the bass to the subwoofer.  It will just pass-through the left/right signal to only the main left/right speakers. You may want to start reading the documentation for your Onkyo receiver.  You might be able to switch to a different decoding mode (such as Dolby Music or DTS:Neural:X).

You can go headphone out to aux in. Seriously crappy. Or USB out to a DAC to aux in. Garden variety crappy. But I believe that you will be impressed.

Cannot advise on sub without info.

Thanks Paleo12 and Sfar, very much appreciate your help.

The computer and mobile phone connected to the receiver is not a problem now, but I suddenly found that the subwoofer sound is very small, when I use the mobile phone to use the 3.5mm to RCA cable to connect to the receiver to play music or listen to the FM radio, The left and right speakers can hear the bass, but the subwoofer is similar to none, the sound is very weak, I don't know why. Is the subwoofer broken?

The Onkyo HT-R290 is a receiver, not a power amp. It has several inputs on the back you could use to connect your devices with the necessary cables. Or, a simple way to connect your phone would be to buy a Bluetooth receiver that plugs into one of your receiver analog inputs with a cable and transmit the music wirelessly from your phone or computer to the Bluetooth receiver. If the computer doesn't have the capability to transmit Bluetooth but has a headphone jack you could use a cable that has a stereo mini plug on one end to fit the headphone jack and two RCA jacks on the other end to plug into the analog audio input on the receiver. Same with the phone, if it has a standard headphone jack you could use the same cable to plug it in.

Hi,

In my experience, one would normally connect a pre-amp to a power amp, and then connect all sources to the pre-amp.  I connected my phone to my pre-amp using a cable from the head phone output to a pre-amp input.  My computer has two options: digital output to DAC, then to pre-amp, or analogue output from the sound card to the pre-amp.