Yes definitely try without that old amplifier, bypass it completely, they were old ones for analog channels and usually amplified noise too much. Unless its specifically for digital cable it can mess up a lot of digital/HD channels they are probably higher frequency than it is designed for. Also a special bi-directional low noise amplifer is the only type suitable for digital cable. You may not need an amplifer at all unless you have a lot of splitters.
Test with that amplifier removed and also remove splitters too for a test. If it works well without them, then you know signal loss from that extra stuff is the culprit and you can then work on replacing them with whats needed and suitable for your setup.
When I upgraded to digital/HD cable a few years ago I had similar junk and took it all out and optimized the signals with new splitters and a good Electroline low noise cable amplifirer I got with a good price on EBAY. That solved all my HD signal cable problems even with 20 year old lossy RG59 internal cabling in the house walls that I can't replace!
I recently checked out my relatives' house cable situation and they also had sub-par signals for digital cable. Had to remove an ancient amplifer and splitter up in their dusty old attic that were only rated for 450Mhz or so, that was OK for 20 years ago for analog only cable, but modern digital/HD cable goes to about 800Mhz. Just took out the old amplifer and replaced an ancient 4way splitter with a 2way (thats all that was really being used) and the higher frequency HD signals suddenly all came in!