The Blon earpiece connector is square, so it won't fit into a round QDC connector. Sanding round the connector corners on the Blon earpiece has worked to use a QDC cable, but you could take off too much material - or it could wear over time - and the cable might not be connected solidly. The pins may or may not be the right length to fit well into the Blon socket - or connected in the correct phase, I haven't tried this work around. Here's a Youtube video on how to modify the Blon earpiece connector:
Link
A 2-pin cable will "fit", but the pins are without a connector - so the whole affair sticks out leaving the Blon connector uncovered. Worse yet the straight-out design of a 2-pin connector sticks the cable straight up instead of the Blon curved designed connector which drapes the cable over the ears.
A TFZ cable connector which is also squarish inside like the Blon connector looks like it would work, but the TFZ when connected doesn't go all the way in and sticks out as well.
This video shows both 2-pin and TFZ type "Blon replacement cable" solutions and how they don't quite fit "exactly" right:
Link
There are 3 versions of Blon replacement cable I've found, all with 3.5mm, no option for a 2.5mm balanced version:
https://www.amazon.com/Earphone-Replacement-****-Earphones-Blon-03/dp/B081H1RHZ5
https://www.amazon.com/****-Earphones-Earbuds-Earphone-Replacement/dp/B081GZV9FM
https://hifigo.com/products/blon-bl-03-4-core-single-crystal-copper-upgraded-cable
Here's a review for one of the 3.5mm **** Blon replacement cables:
Link
It would be nice if this **** 16-core cable - or maybe an 8-core cable - were offered with Blon earpiece connectors:
https://hifigo.com/products/****-16...-5-4-4mm-upgrade-cable?variant=31205718786097
A 16 core cable might be a bit heavy for the Blon-03 to hold in, but moving from a Medium to a Large foam tip has anchored in the Blon BL-03 for me nicely.