Is There Greener Grass For Me?

I have owned an Onkyo TXSV515PRO for about 15 years. I have upgraded most other components in a modest AV system, but not the Onkyo. We use the AV system for audio only as it relates to TV programming and DVD play – there is no CDP involved – all music being played in a separate, dedicated 2-channel room.

Currently, the system consists of:
TV - Mitsubishi WS-65413 – 65” projection
Front Speakers – PSB Stratus Goldi’s
Rear Speakers – PSB Alpha Mini
Center Channel (own but not currently used) – PSB 9C
DVD - Zenith DVB318

Now. I am not trying to assemble a SOTA system in any way, shape, or form. However, I do not care much for the separation provided by the Onkyo, especially front to rear balance (regardless of how the speakers are positioned). Too, if something like a great performance on Soundstage or an audio DVD is used, the sound is a bit thin when cranking the volume. I’ve had these speakers in two-channel systems and they are not exactly what I’d call thin. As such, I am wondering if I could improve things much by using a different power/processor – or maybe given the level of all else I should just leave things alone.. I’d STRONGLY prefer a one-piece unit, as opposed to separates, due in part to space limitations. Don’t need a tuner which is provided in the Onkyo receiver. Appreciate suggestions in the $2K new, $1K used range. Obliged to all for their consideration – whether or not you choose to respond.