Deuce, consider that before the advent of Lionel Railsounds in 1995 (or there about), that is the sound that most diesel trains had. In the postwar diesels, it was a bicycle buzzer. I'm sure to most kids, this was a sufficient sound, but there were no other options and nothing else to compare it to, other than the real thing. But kids used and still use their imaginations. With today's modern toys, we kind of kill the imaginations of children with all the electronic do-dads. When I was a kid, you got a Tonka Truck that made no sounds, but did in your imagination. Today, that toy truck has sounds and lights, but when those stop working, it ends up being tossed to the trash.
That said, you can experiment by placing a short cone in front of the speaker in that sound shed. I did that with mine, and it does improve the sound. But it is still more of a buzzer sound than that of an actual train horn sound.
From an economy angle, years I ago I purchased a couple of MRC Sound Stations for $20 each when they were being blown out. These are self-contained, wall-wart powered sound units with a push button controller and two speakers. They have a whole variety of train sounds, from horns and whistles, to crossing gates and conductors. They are more for HO, but I wired in a couple of old boombox speakers, which got the sounds much louder. Lionel Railsounds it is not, as the sounds are not sequenced to the trains (like with the steam chuff). But the sounds are fairly realistic and the push button activation is a real kid pleaser - as I have found in my experience. One child can have the throttle of the transformer while another can activate various sound effects.
The nice thing about off-engine sounds, is that you have sounds for everything. And some of the more affordable train engines today on the secondary market, do not have sounds on them.
On the other hand, if you are used to sounds coming from the trains themselves, it might not suffice. The sounds coming from even the LionChief train sets are impressive for a starter set. And since you have a LionChief set, this might already be the expectation your boy has.
One more option is the Lionel Railsounds box cars, that have not been made for some years now, since everything today now comes sound equipped. But there were box cars with Railsounds units installed in them for either steam or diesel, so that you could run a postwar or modern loco that didn't have any sounds. You can locate these on the secondary market.
