Sempaul, Tough to give them up, isn't it? I own a pair of JBL L112s. I purchased them new in 1981. To this day, anytime I hook those speakers up and play them, I just sit there with my mouth hanging open. It is unreal how good those speakers sound. I keep saying I'm gonna sell them, but I just cannot bring myself to do it! The L150s are great speakers, although they are somewhat intrusive in size.
Tomryan is el correcto. Speaker tech has changed a real lot in the last 23 years.
But, one thing has not changed. The fact that many of the older classic speakers sound great. Depending on your room size, you may not need to actually use a sub, considering you will have four twelve's firing at you. Now the problem starts when you try to match a center and rear speakers in regards to timbral characteristics.
I feel, HTs sound better when using a set of matched speakers. At least having your L/R front and L/R rear speakers matching. And when using speakers designed and built by one manufacturer, in most cases, they have taken time to make sure the speakers have at least a timbral match, although the speakers may differ in actual configuration.
And, I hate to say this but, you may find that the only way you're going to find a center speaker to seam with your main speakers is by trial and error.
Hey, I just had an idea. Look for two more L150s! Then try some vibrapods under the legs of your couch. Maybe the floor shaking won't be so annoying to your wife (as long as she stays on the couch). And if your breaking windows with those speakers, an annual hearing check may be in order. Good Luck!