@brandini,
Moving from your existing lightweight Onkyo receiver to a dedicated amplifier for your Ascend/RAAL speakers can be a worthy step up IF you choose well. It seems your Topping D90 offers (dual-active) preamp outputs (XLR & RCA), so you could actually run one set of XLRs to your amp, and the other set of RCAs to the sub. As you may be aware, lower model Rhythmik sub amps offer only RCA inputs, upper models offer XLR, if you wanted to flip it and run XLR/balanced to the RA sub. Not sure which RA sub/amp you have.
AMP & Budget;
Class A/AB, your (4ohm) speakers deserve a good stable amp with some real (weighty) transformer(s), and capability to run lower impedance swings with ease. The Frank Van Alstine AVA SET 400, w/optional XLR comes close at your top budget. Class D Purify, such as your thought about the NAD C298 could work too in terms of power and budget, sound is up to you. I’ve been considering testing both of these in a secondary setup.
Taking your time to research and secure a really good amp will pay off.
Ask amp manufactures first about your Topping D90 Balanced/XLR output voltage at 4 volts:
"Dual output ports:"
"Topping D90 is equipped with dual output sockets, XLR outputs offer 4Vrms output power at 0dBps, and the other output port, an unbalanced RCA offers 2Vrms output power at 0dBps. It provides enough power to power any of your demanding devices, whether it’s headphones or a speaker system. The D90 can send a signal through both output ports at the same time, so you can use multiple tools at the same time. It is equipped with a volume control function, so it can be used both as a digital-to-analog converter and as a preamplifier converter. The volume control can be turned off so that the D90 works only as a digital-to-analog converter."
Moving from your existing lightweight Onkyo receiver to a dedicated amplifier for your Ascend/RAAL speakers can be a worthy step up IF you choose well. It seems your Topping D90 offers (dual-active) preamp outputs (XLR & RCA), so you could actually run one set of XLRs to your amp, and the other set of RCAs to the sub. As you may be aware, lower model Rhythmik sub amps offer only RCA inputs, upper models offer XLR, if you wanted to flip it and run XLR/balanced to the RA sub. Not sure which RA sub/amp you have.
AMP & Budget;
Class A/AB, your (4ohm) speakers deserve a good stable amp with some real (weighty) transformer(s), and capability to run lower impedance swings with ease. The Frank Van Alstine AVA SET 400, w/optional XLR comes close at your top budget. Class D Purify, such as your thought about the NAD C298 could work too in terms of power and budget, sound is up to you. I’ve been considering testing both of these in a secondary setup.
Taking your time to research and secure a really good amp will pay off.
Ask amp manufactures first about your Topping D90 Balanced/XLR output voltage at 4 volts:
"Dual output ports:"
"Topping D90 is equipped with dual output sockets, XLR outputs offer 4Vrms output power at 0dBps, and the other output port, an unbalanced RCA offers 2Vrms output power at 0dBps. It provides enough power to power any of your demanding devices, whether it’s headphones or a speaker system. The D90 can send a signal through both output ports at the same time, so you can use multiple tools at the same time. It is equipped with a volume control function, so it can be used both as a digital-to-analog converter and as a preamplifier converter. The volume control can be turned off so that the D90 works only as a digital-to-analog converter."