Generally speaking, you can get Bluetooth Capability for any where from $25 up to $500. Though you can do very well in the $50 to $75 range, again depending on what you specifically want.
Assuming you want to receiver from an external device and play through the Kenwood, that is easy enough.
I most often recommend Avantree as they seem pretty good and have long range and low latency (delay). The Oasis and the Oasis HD are about $50 each and $75 each, though the HD seem in short supply right now.
Amazon product ASIN B01N2VKCO0
Amazon product ASIN B07WW3ZHTQ
These device are both Receivers
(Phone to Amp) and Transmitter (Amp to Headphones).
Here is th
e HD or Plus version of the Avantree Oasis -
Amazon product ASIN B07BQYYDNJ
Generally all you need to Receiver is a spare unused RCA Input
(CD, AUX, TAPE, etc...), connect the Bluetooth Receiver to the Amp, PAIR the devices and you are ready to go.
To Transmit, say to remote speaker or headphones, you need an output from the Amp. I suspect a TAPE OUT would work.
Not really that complicated.About the same as connecting a CD Player.
To Play from a remote device, simple select the appropriate input. For example, if you connect Bluetooth to AUX, just select AUX and you are ready to go.
If you search Amazon, you will find a near infinite number of Bluetooth Receivers to choose from -
Amazon-UK Search - Bluetooth Receivers
If money is tight, there is a device that is both Receiver and Transmitter and supports Bluetooth 5.0, which is the current standard, and it costs £29 -
Amazon product ASIN B07J58KY3X
Here is a Bluetooth Tx/Rx 5.0 for £17 -
Bluetooth Adapter Bluetooth Transmitter Receiver 5.0, 2 in 1 Wireless Bluetooth Receiver Audio Adapter AUX Compatible Low Latency HD Sound for PC,TV,Smartphone,Tablet, Home Stereo System, RCA/3.5mm: Amazon.co.uk: Computers & Accessories
Typically a standard Bluetooth Tx/Rx has a range of about 30ft (10m) line of sight. However, the long range models like Avantree (and others) have an extended range of about 75ft (23m) to 100ft (30m) generally line of sight. With some reaching as far as 50m.
Generally and devices that has Bluetooth 4.0 or above is going to be good.
Now, if you have a bit more money, you can get Full Network Streaming for about £150 -
Yamaha WXAD-10 Network Streaming -
Free delivery and returns on eligible orders. Buy Yamaha WXAD10 Wireless Streaming Adapter at Amazon UK.
www.amazon.co.uk
So, you have a range of options.
Steve/bluewizard