Decent preamp

Croft IMO is the most bang for the buck in Audio .

Visit your local retailer. He will take into account your room size, your speakers, your listening habits, how you listen, what products make sense for you. I always buy 50% more power as a rule so you can have Dynamic range. This way your electronics breathe easily. Make sure you have lots of ventilation, clean the unit every year completely. Remove all cables and clean the ends. using Dioxit and other similar products will help. 

Just another way to look at all this. When I listen to the identical preamp you already have into a  McIntosh amp with the exact same output as your Aragon 2004 I experience a pretty extraordinary performance on all fronts with exceptional accuracy, clarity and separation. You may possibly be trying to improve the wrong end of your system. Just a thought.

here’s a classic Eico, a bit over budget, $750. returns accepted. Has 2 phono inputs, and mode switch like McIntosh preamps do, many other features modern preamps have dropped, i.e. more inputs, balance, tones, loudness compensation for low volume listening ...

https://www.ebay.com/itm/Eico-ST-84-12AX7-6X4-Tube-Preamp-Stereo-Pre-Amplifier/233560836018?hash=item36614f87b2%3Ag%3AXcEAAOSwMmhel7om&LH_BIN=1&LH_RPA=1

have a look at it's innards, looks very easy to replace anything that goes in the future, very easy to spray clean all the controls ...

where are you?  I'm in Plainfield, NJ, 07062

If close to me, I have 3 fisher 500c tube receivers, all working, I could verify one in my system and let you try it, keep or return it. no shipping helps a lot on these old dogs.

stay 10 feet away, (we're retired, haven't been out for weeks)