What is my next step to a better sound ?

I am looking for educated opinions from audiophiles that have owned are listened to systems similar to mine.

I have a Mark Levinson no.380 preamp and a ML no.334 amp with Watt Puppy 5.1 speakers,serie 7 tweeters.Arcam Rdac with Teddy Pardo power supply.Transparent plus cables and MIT shotgun xlr interconnects.

I really am not sure what component i need to change to step up the ladder towards a better HIFI sound.

Preamp ? Ml 380 S ? 326 S ? or maybe another make ?

I was suggested to change my preamp for a SPECTRAL 15

My transport is a 250$ Sony bluray player ,i dont believe that buying anything more expensive will hep with the sound ,its going through DAC anyway,correct me if you think im wrong.

I listen to Bluaudio and SACD SHM.
The rDAC is easily the bottleneck in the system. It's a great DAC for the money, but it just doesn't belong in your system IMO.

I really like the rDAC. It's outclassed by the rest of your gear.
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ditto Elizabeth and Kbarkamian!
As you may know, there are many threads on audiogon on source vs. speakers. Even articles in past audiophile publications where CEO's of Wilson Loudspeakers and Linn debate the question. I believe both have a very valid point. Ignore one, and you will not get the most out of your system. I argue there has to be a balance, and it is definitively tipped in your case. Given that you listen mostly to blue audio and SACD, I would strongly consider the newest offerings from Oppo (BDP-95), or used Modwright modified (or by other established modders like EVS) Oppo BDP 83SE. You would be in for a real treat.
Do not change your preamp for a Spectral. Besides creating a mismatch if you ever need service on the Spectral you will have to deal with Spectral and to me it's not worth it.

You need to upgrade your CD player. To match your system you could consider a Mark Levinson or Audio Research CD player. Either one will breathe some life into your system.