Define "substantial amount". Did the military tactic involve artillery barrages followed by musket ranks? Or was it still mainly concentrated on cavalry charges, infantry spearmen and archers?
Ming prefers artillery rather than musket because musket does not outperforms traditional crossbow and archery -- crossbow was the standard infantry equipment. Compare to matchlock musket at the time, crossbow is a better weapon because it has higher rate of fire and is more accurate. Ming artillery contains a substantial portion of breech loader -- which increase the rate of fire.
Your Qing idea doesn't hold water. Every dynasty, from Han forward, is obsessed with centralizing power. Ming emperors faced many peasant revolts even before its decline. Yet, according to your previous statement, the Ming were quite adept with firearms.
Han outnumber Manchurians in the order of 100 to 1 -- the only advantage Manchurians has is cavalry and archery. Firearms took away that advantage. Manchurian also face Ming's firearm, and it does not want to face that again. Since firearm requires less skill to use effectively than archery, this make rebellions less of a threat if firearms are not available. Note also the crossbows, which has been the main Chinese weapon from Warring States period to Ming are gone as well.
Manchurians also regards martial skills as birthright and are chauvinistic about archery, so they deliberately de-emphasis firearm.
I disagree with this explanation. The Song dynasty was nowhere near being the strongest kid on the block. The most prosperous, yes, the strongest, no. Ming empire faced threats and challenges on several fronts: the Yuan in the North, and the Japanese pirates along the eastern coast.
If military challenges were the defining motivator, China had plenty of motivation to develop better firearms throughout the centuries.
Strangely enough, Emperor Kangxi of the Qing did put a lot of emphasis on building cannons, yet this was for some reason abandoned later on. Further, the Chinese never seemed to have envisioned firearms as a primary personal weapon (i.e. rifles and pistols).
The main military problem China faces was it is deficient in cavalry -- lack of horses, while the barbarians can pretty much mount their whole troops. So the main military emphasis is anti-cavalry. Since firearms of the period is not accurate, it is of limited use. Against infantry, breech loading artillery works as well if not better, compare to muskets -- so classical musket tactics didn't get developed. However, this was no great loss, as crossbows was already doing the same job.
Against Japanese pirates, Chinese developed a weapons team tactics -- patrol ground armed with long arms, blades, and firearm. In this case, the range is short enough for firearm to be effective -- long arms and melee weapon protect the firearm while it loads and shoot.
Kangxi builds cannon because he was faced with a rebellion and need seige weapons. After the rebellion is suppressed, Manchurians went happily back to cavalry.
Essentially the Ming developed firearms because it was mainly an infantry army. Manchurian Qing does not like firearms because it has a cavalry army and firearms are not easy to use on horseback.