If you want a real life, inexpensive preview of what eliminating your pre-amp may sound like, take a look at tweakaudio.com where the Ultimate Attenuators are sold.
These are plugged directly into amp RCA input jacks, acting solely as stepped volume controls, and eliminating separate pre-amp with its pair of interconnects presently in the signal path. Ultimate Attenuators seem sonically invisible.
Allows for any CDP, even one with fixed analog outputs.
There is a model for either transistor, or tube amp.
Rather than simply running direct, when the pre-amp was gone, I discovered the SCE Harmonic Recovery box which better optimized the transfer of analog musical information exiting my CDP. So, in the end one pre-amp box was discarded, only to be replaced with one SCE Harmonic Recovery box. The payoff was getting audibly better sound than with either the original pre-amp, or with no pre-amp. Just one way that one change may lead to another.