There has been an incident and I need advice

There has been an incident and I need advice

I was in the midst of upgrading my system to higher fidelity equipment. I had run a pair of Cerwin Vega D6s with a Carver M400 cube from a Nikko Beta 30 Preamp. All the equipment was circa 1978 or so :>). I listen mostly to CDs and selective rock FM. I am willing to go away from classic 2 channel equipment to incorporate HT but it is not required.

I first lost the carver and decided not to have it repaired. I replaced it with a Adcom GF 555 and then added a Velodyne SPL 1500 subwooker and I was really pleased. I had been looking at floor standing speaker upgrades. In trying to utilize the velodyne’s crossover I think I shorted the Nikko Pream at the plug and I was severely shocked and am terrible depression for no tunes.

Can anyone help guide me to a replacement preamp and make a suggestion on speaker upgrade. My budget can vary greatly but I don’t think I am yet ready for Krell or other, or maybe I am . I am not afraid of used equipment especially if the source comes from this board.

Thanks for reading and any input.
Seeing that you've already acquired an Adcom amplifier, the Adcom GFP750 would seem to be a logical mate. I'm not sure how it compares to the Nikko, but it is very well worth the $6-700 you'll spend.
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I had a CJ PV-10B matched with an Adcom 555 for years. It's a great preamp, and the CJ/Adcom combo makes some great sound. Plus it can be had for a good price here on Audiogon.
GFA 555 is very fast and forward try an older Conrad Johnson preamp to smooth things out, just make sure it has a L-R balance control
I say Adcom GFP 565. In fact there is one for sale here $250 wow. There are a couple 555's around that I know of as low as $175.
Adcom 750 pre has my vote as well, if you want SS VTL has a well regarded entry level tube pre that does a good job... so does BAT. they go for about 900-1200 respectively.

speakerwise, as you have the SPL already, and not knowing budget or room parameters, perhaps Silverline Sonatina's? Phase Tech also makes some fine inexpensive speakers and have been making them for decades.